Although these are guides, the author does not advise anyone to actually build or even consider building such devices. Read, but do not act upon this information. Everyone should just live a quiet, pastoral life because the dogs of law lie around every corner and I have no wish to be closed down like other useful websites from threats by parasitic lawyers. (When lawyers get rich, society gets poorer.)

Always try to improve society rather than just take from it. Until then, lawyer stuff. Contents for illustrative purposes only. All material herein is subject to copyright, patent and other intellectual property rights. Copying, duplication or transmission of this material whole or in part is not permitted without the written permission of the author. Contents subject to change without notice. Errors and omissions excepted. All rights reserved. No responsibility is accepted for any damage or any injury caused by this information. No-one should try building machines without reasonable abilities and know that injuries can ensue from the materials, tools and from test riding of machines.
Copyright (C) J.Partridge. 1985. 1998. 2003.

The author would like a job. A long term unemployed, motorcycle mechanic, draughtsman, plant engineer, marine engineer, technology teacher and science graduate. Please consider this monograph a C.V.

Introduction.

Wiring a motorcycle, trike or car is not expensive and only needs a little time and knowledge of the subject to get the basics right. Once the basics are right, the rest becomes fairly straightforward. The wiring of a car has been added where appropriate, as it is usually easier, apart from the engine management and computer systems.

This is not a definitive work on all the various and somewhat dubious electronics or other strange components which contain a wire or two and used on vehicles. This beginners guide is also to act in a support role for the other builders guides.
This monograph includes what is needed for road legal requirements, with extras added for the normal adaptations and flourishes required for customs and unusual machines. This is based on first hand knowledge of building award winning and reliable custom bikes and trikes for over twenty years, plus many radical machines as well.
A storyline wiring guide for Harley owners is also on this website.
The subtle and far more delicate development of HPV cycle wiring is described in the composite HPV cycle monograph by the author.

The advantage of doing the wiring oneself is that it is tailor made and can be easily modified. When things go wrong, the fault finding and repair can be done by the rider, on the side of the road, usually with minimal delay.
The aims of the monograph is to remove the mystery of motorcycle wiring, to enable the reader to rewire without specialist abilities.
Trike wiring is very similar, with differences described where needed.
Car wring for the more sensible customs is simply separating and adding the engine management systems, then doing the rest of the wiring using traditional methods described herein.

The main aim is to design and make a wiring loom to a standard every bit as good as the best customs. This is done by initially keeping the process on the most basic level needed for the purpose. Only when the basic wiring is reliable, should the reader consider adding flourishes.

If some of the explanations given seem really simple, please bear with this, as there are absolute beginners out there who need the simple explanations to make everything understandable. We were all beginners once.
It is assumed the reader has almost no knowledge of electrics. This is to make it as simple as possible to wire a bike, trike or basic car. Therefore this monograph is not a complete technical manual, as to make such a tome would require many volumes, loads of theory and maths. This would simply confuse more than it would encourage, probably having most bike builders throwing it in the trash or through a window.

This monograph is mainly for a total rewire, starting from scratch, as this is surprisingly much easier to understand and then build. The text was originally mainly for Japanese bikes, as they had effectively set the present standards for wiring vehicles, with sections on others where needed. The Italians are now set to overtake the Japanese - watch this space.
Trikes and custom cars often have lower specifications and needs.

One thing needed to go with this text is the wiring diagram for your particular vehicle. Trikes rarely have such luxuries but motorcycles and cars have the workshop manual. I've drawn some generic wiring diagrams for the unlucky.
Without a wiring diagram, you will need to follow the text to find out what wires go where. Then note down on paper where they go, what they do and their colours. An A3 sketch pad and pencil is priceless. If your motorcycle or vehicle has no wiring at all, then choose the wiring diagram to match the engine rather than the bike.
Use the diagrams accompanying this monograph to get a close match if you can't get a wiring diagram. A selection of basic, generic diagrams are given at the end of the monograph. These are done at a large scale suitable for printing or as a starting point for using in a paint programme for modification as needed. They can be copied and pasted or imported into a paint programme size of 800 x 600 pixels in black and white, although the incredibly simple Harley one is in colour.

This text is not one of chasing particular colours of wires, but to understand the basics of where the wires come from, where they go to, and what they do. - For example, a typical description of 'the alternator wire' means a wire connected to the alternator, not a specific colour of wire to be chased by someone who is not too sure, but a simple electrical connection of a wire. When you know the alternator, you will know the wire and what it does.

Safety and working practice.

When beginning a total rewire, make life easier for yourself. Get some plastic bags to hold the parts, preventing them from rusting or getting lost. Keep all parts, no matter how bad, and run a clean, neat workspace.

The worst case scenario is a totally burnt out wreck of a bike, with dubious heritage and a different engine to standard. Don't panic.
The electricity and sparks are generated by the engine and this is where you start. The rest of the wiring on the bike will follow naturally. It is quite common to use completely different components from other machines to make a perfectly reliable machine.

Before removing the wiring, make a note of which side of the battery is connected directly to the frame or chassis. If it's on the positive side (+) then you have a fairly old or peculiar bike or car, and you will have to bear in mind that this book is directed at modern machines which have negative earth systems, (-) but are much the same in most other respects.

What your vehicle needs - the basics.

What your vehicle needs - the law.

Know your countries requirements to live in harmony with your local form of 'normality'. Your vote counts. Never give your vote to someone who wants type approval or other stupid ways of excessively controlling the people, their machines and their aspirations.

There are also regulations concerning radio interference, so the bike will not cause interference with other equipment. The main culprits are the spark plugs which can be shielded with metal caps and a resistor in the plug or in the cap (but not both).

The Basic Words and Theory.

Circuit.

Earth.

Open Circuit.

Short Circuit.

Fuse.

Wire.

Amps.

Volts.

Watts.

Example . . 5 amps x 12 volts = 60 watts and so this basic headlamp circuit will need at least a 5 amp fuse to protect it, usually a 7 amp fuse for the normal safety margin to prevent it blowing too easily.

Spark Plugs.

Coils.

Generator coils.
These live in the generator and produce electricity from magnetism. Here is an example of a basic lighting coil which will happily supply lighting for a head and tail light. This item produces AC current, which may then be recitifed and regulated to 12 volt DC. For lighting use only, it can be used as unrefined AC current, with no other consideration other than balancing the power of the lamps, so as not to blow them at full engine revs. If the lights blow, fit larger voltage or wattage lamps.

Contact Breakers.

Condenser.

Advance / Retard Unit.

Battery.

Starter Motor.

Starter Solenoid.

Alternator.

AC and DC.

Rectifier.

On small bikes, just one diode can keep costs very low which only uses half the AC current, but usually manages to charge up the battery on bikes, where the main AC current is used to power AC lighting.

(A standard 12 volt 36 watt lamp can use 3 amps of AC or DC current to light equsally well.)

The simplest is a single diode for charging a battery on a small bike. for larger machines, then four diodes are used and the animation shows how alternating AC current flow is changed to DC direct current flow at the red and green. The diodes are acting like one way valves and this is how they are also checked.

Regulator.

Dynamo.

Electronic Ignition.

Fuel Injection.

Engine Management System.

Loom.

Connectors.

Soldering is used where a wire needs to go to two places at once, such as the lighting wire going to the tail light as well as the headlight dip switch. Strip the plastic insulation back about 5mm, twist the copper inner wires together and solder them until the solder flows freely to make a good join, then clean off the flux and cover using either insulating tape or heatshrink sleeving. Some big Japanese manufacturers do not remove flux whereupon corrosion can occur early and some have been known to fail within three years of leaving the factory.

All connectors on the battery side must be shielded so that if one becomes loose and separates, then the bare end will not short out against the frame or engine, this is done by using the connector half which uses the full length insulating sleeve.
It is for this reason that even the simplest component such as a brake switch will have a male and a female connector. The shielded connector should be the 'live' one.

Why have connectors when it's simpler to just twist the wires together and tape over them? It's simple to do, but annoying when you have to take it apart again and still remember where they go. If you are going to keep the bike, or wiring it for someone who will, then do it right first time, with no further problems.

Heatshrink.

Switch Types.

A switch which connects two contacts together and stays in place, as used for the lights switch, is a simple on/off type known as 'single pole, single throw ' switch (SPST). This switch can 'throw' one way or the other, and can be used for the dip switch to send the electricity to either the high or low beam.

The switch used for the indicators needs to connect the wire from the flasher unit to the left side contact for the left indicators or to the right contact for the right indicators. This is a single pole double throw. (SPDT) It can switch one wire (pole) either of two ways. The centre position usually does nothing.

Imagine two SPDT switches, connect them side by side and working off one lever, this is a 'double pole, double throw' switch, (DPDT).

Ignition Switch.

Oil Pressure Switch.

Oil Level Switch.

Car switches.

The indicator switch is probably the hardest to get half decent, but there are a few dash mounted types available. If a pair of push buttons are used, then a switch in the steering can be used for the off switch, with a little electronics and a distance timer for safety switch off.

Car Ignition Switch.

Relays.

Headlights.

Tail Lights.

Fog Lights.

Spot Lights.

Wiper motors.

A Guide To The Wiring Diagram.

A wiring diagram is like a London underground map, ( a classic piece of design) as it is a schematic. That is to say it approximates to the layout of the actual item. For wiring diagrams, the description 'approximate' takes many liberties. These liberties usually make for an easier to read drawing.
To understand a wiring diagram, the main signposts must be recognised. The lights, battery and switches are simple. The rest of the gaps can be filled in with a little time studying the drawing.
The small squares where some wires cross, represents an electrical connection, often a soldered joint, although it can mean any other method which manages to do the same. All other wires cross independent of one another. Where the tail light assembly and the handlebar switch is removable from the loom, the two rectangles represent the multi-pin connector.

One concept can be represented many ways. The earth connection symbols can vary from a representation of a tag to bolt to the frame, to a line entering a solid surface or a spike into the ground.
A single symbol can represent many different items. The diode symbol may represent a single diode, or a more complex electronic device such as a rectifier/regulator unit.

There is a trend in the car market towards totally unreadable wiring diagrams, often based on a numbering system. This may be acceptable for manufacturers who simply describe and replace parts, but is not remotely usable in the real world. Always draw a wiring diagram schematically, so it can be followed logically. If a very complex wiring loom is needed, then simply break the wiring down into discrete chunks, drawing each system on a separate sheet. Do not follow car practice and have many cross points to save a few wires, but make stand-alone circuits, independent and robust in their operation and reliability.

Hidden in this mess is usually only four different circuits. These are the charging circuit, to generate and store the electricity. The ignition circuit, to start and run the engine. The lighting circuit. The auxiliary circuit.

How to read a wiring diagram. Only the modern car wiring diagrams seem to be designed to be incomprehensible. For most vehicles, a wiring diagram can be read easily, if you know the language. It's usually in an anorak form of English.
Although you may have a specific problem to overcome, take some tie to understand the layout. Start with the battery and ignition switch and fuse box. From these, the various other components can be discerned, then the wiring leading to and from them.

As all wiring diagrams are different, the following guide is common to most modern motorcycles. If yours is very different then tread carefully, but the differences are usually small, as there is only certain things that can be done with wiring.

Typical alternator symbols are from left to right, star wound, delta wound, two separate coils ( as on most small bikes) and a symbol of a sine wave, as generated by an alternator.

For example if the whole of the lighting circuit is white, then a white wire with a red tracer showing that this particular wire goes to the tail light (W/R) and a white with blue tracer to the main beam (W/BU). The builder of a custom machine may prefer to use colours which are easily understood. In this case, the tail light is red, hence a red tracer. This is not standardised for most vehicles, but can make life easier if designing your own wiring.

Colours are standardised for each manufacturer, an earth lead on a Kawasaki will be the same colour on another Kawasaki, but not necessarily the same colour on a Yamaha. Distinct circuits are often given standard colours eg: all earth wires are the same colour.

After a basic understanding of the components, now to put them together. A guide to where electricity starts on the machine, to where it ends up.

The Alternator And Charging Circuit.

The magnetic field can be made using permanent magnets or by using electricity in a 'field coil'.
The AC electricity produced is changed to DC electricity (direct current) by a device called a rectifier which is then regulated to about 14 volts for a 12 V bike. (7 volts for a 6V bike).
This DC electricity can then be used to charge up the battery and supply the lights etc.

If you put 12 volts across a 12v battery nothing will happen, if you more volts across the battery, then there will be enough difference in voltage to cause electricity to flow and charge the battery. Too much voltage will slowly cause the battery to heat up and dry out, eventually causing damage and bulbs to blow. Too little voltage will not allow the battery to be charged.

Some bikes will have alternators similar to cars, which are usually open to the air with cooling slots. These are often self contained units delivering 'ready to use' DC voltage and so the alternator sections below will be superfluous.

Check your wiring diagram or use one from the selection at the end of the monograph. Find the alternator which is usually shown as circle with symbols representing coils of wire, these are often as a triangle or a wide 'Y'. An 'S' shape on it's side can also denote alternating current.
On most bikes, usually look for two or three white or yellow wires.
Larger bikes with traditional alternators will have three white or yellow wires coming from the corners of a triangle or 'Y' star of coils. On a few rare machines there may also be a field coil with one side connected to earth, the other wire going to the regulator.

When the engine is opened up, there may be nothing remotely similar to the wiring diagram, as it is a 'schematic'. The actual components are usually resin covered lumps of copper wound over steel plates riveted together.
Check for any physical damage. If damaged, either carefully deconstruct and rewind with identical varnished copper wire or have it rewound commercially or replace. See later. The wires coming out from this device are the main areas of concern. The two or three yellow or white wires can be easily replaced.
The small steel arms wound with copper are the alternator windings, and can be from just one winding the size of a thumb for a moped, to a dozen smaller items on some big bikes. All sizes and shapes available.
The rotating flywheel will contain permanent magnets which will attract steel tools. Clean off any excess magnetic debris or rust. If there are no permanent magnets, then there will be a big bobbin of wire in the middle, this is the field coil.

The two or three yellow or white wires will go to the rectifier. This usually also contains the regulator. The rectifier is a simple bank of diodes which allow the alternating current to be rectified so it all comes out 'flowing in one direction' as DC direct current.
The rectifier has the white or yellow wires going in, and a red wire coming out, plus an earth wire, or is earthed via a mounting bolt or its metal casing.
If the rectifier and regulator are separate, then the rectifier output wire will go to the regulator. The regulator constantly regulates the voltage at approx 14 volts.
The output from the rectifier/regulator will go to the battery, supplying the 14volts DC ready to charge the battery and supply the rest of the bike.
The regulator may have an earth wire, denoted by its colour. Where appropriate, always make sure the finned metal body of the regulator is well earthed via its mounting bolts.

The regulator may also have a sense wire. A sense wire is usually slightly smaller, which is used to sense the voltage in the main loom. This allows the regulator to keep the voltage correct. This sense wire should be connected to the output side of the ignition switch, usually where it joins the three fuses. If fitted, do not connect this wire on the main fuse side of the ignition switch.

Holding the regulator or the remains of a regulator in your hand, the two or three white or yellow wires are easily recognised. Then the thick red wire, again easy to see. The earth wire, if fitted will be the same size as the red wire. Any other wires will be the sense wire, or if the original engine of this rectifier has a field coil the any left over wire is almost certainly the field coil wire. If no field coil then it's probably a sense wire.

If the alternator has a field coil, the regulator will have an extra wire and this wire must be connected to the field coil. Check by comparing the colours of the wire from the field coil to match any on the regulator unit. An alternator with a field coil must use a regulator for the field coil type. If in doubt, check with original wiring diagram for the specific bike. This wire will usually be routed beside the three white or yellow wires, entering the alternator, and going to the bobbin of wire in the centre of the alternator. As the engine revs more, the alternator pumps out more electricity, so the field coil is lessened, keeping the output steady. If the lights are switched on, the field coil is given more current and up goes the alternator output. A very efficient design.

On a small bike, there may be two separate long straight coils of windings inside the alternator. The one with the thicker copper wires with fewer turns is the winding which generates the battery and lighting electricity. There may be two wires. Probably one white or yellow wire, which often goes directly to the light switch for direct lighting. Another wire will go to the diode to charge the battery. See later. The other coil supplies the sparks and is part of a completely different circuit.

You now know where the electricity comes from. It is generated as AC at around 30volts. This is then changed to 14 volts DC and stored in the battery, ready to be used, so make a sketch for your machine. Draw the alternator, the AC wires to the rectifier and regulator, then to the battery.
Do not forget the earth connections on the rectifier / regulator and the earth wire from the battery to the frame to complete their circuits.

The battery has an earth wire usually on the negative side and this goes to the frame. Older bikes may have a positive earth, check first.

If the machine has a starter motor then the earth wire will be a thick cable and may connect directly to the engine crankcase. The positive side of the battery will use a thick cable to a heavy switch called the starter solenoid and from this to the starter motor.

A wire on the positive side of the battery also goes to the main fuse. The main fuse is usually connected close to the battery, so that all subsequent wiring such as those leading to the ignition switch and all other wires are thereby fully protected. Most main fuses on larger bikes and most car-based trikes are about 30 amps.

A wire from the main fuse goes to the ignition switch. From the other side of the ignition switch, a wire goes to the three ignition, lighting and auxiliary circuit fuses.
The ignition switch may also switch parking lights and other components, but is otherwise a simple on off switch, usually with an integral steering lock to deter theft.
As the ignition fuse, lights fuse and auxiliary fuse are often in the same fuse box as the main fuse, the wires will lead from the main fuse to the ignition switch and back again to the fuse box.

Because the wires from the regulator to the battery, from the battery to the main fuse, to the ignition switch and the wire back to the three fuses must carry all the electricity for the bike, it is therefore a little larger than the rest of the wiring. These wires are slightly larger and capable of about 15 to 30 amps depending on the machine.

For those wishing minimal wiring, just the main fuse will do, although if something causes the main fuse to blow, then all the electrical items will stop working. See later.

Small bikes.

This picture shows a C90 rotor with the pulser interrupter on the outer edge, which caused the timing pulse at the right place, and the pulser is the black lump between the rotor and stator. Lying flat is the stator plate with the pale lighting and dark CDI generator coils.

There are four magnets inside the rotor, such that as they pass the stator coils, they induce a changing north - south, then south - north alternating magnetic field in the iron plates of the coils, thereby generating electricity in the copper coils of wire.
As can be seen, the four poles at the ends of the coils means that the magnets in the rotors are four, so the N-S-N-S field flows strongly through the iron cores. This is acceptable for a low power machine, but sometimes a little more electrical power is needed in such a small space, so six poles can be use, with six rotating magnets. Now we are six. The black and white picture shows another popular arrangement, where the lighting coils are the five coarsely wound coils, while the generator is the obviously different one nearest the viewer. Again the pulser is outside. You will also notice that as a six pole stator, the rotor should have six magnets. You can just make out the size and layout of the six magnets inside the rotor.

Although these systems are not perfectly balanced with a constant voltage, the output is such that it will usually do the job. If under powered with a dull glow, simply use a lower wattage headlight bulb. If overpowered and bulbs constantly blow, then fit a larger wattage headlight bulb until the system is 'balanced'.
Another problem is if the battery cannot charge fast enough, then fit lower wattage indicator bulbs (if the law permits) and don't stop with the brake light or indicators on all the time, thus draining the battery. Indicators and brake lights are usually the main culprits which quickly drain the battery on these minimalist systems. Connecting just the rear brake light switch, while disconnecting the front brake light switch often suffices.

Summary.

Why have fuses?

Why have a main fuse if you have three others?
The ignition switch must be protected as it takes all the electricity through it and will be unprotected without the main fuse.

Why not have just one main fuse and forget the rest?
Suppose you're driving along, and a wire on the lights shorts out. - With only a main fuse, all the electrical circuits will stop, including the engine. If you are in a dangerous situation, the last thing you want to happen is to loose all engine power.
If you are riding at night and the engine fuse blows, you don't want the lights to fail at the same time.
By using a main fuse plus three others, there is far less chance of the main fuse blowing first, and all will not fail at once.

A fuse will commit suicide to protect the wiring, when the fuse blows replace it with a new one of the same rating as they sometimes simply just get old and fail. If the new one blows, then it's time to find the fault in the circuit it is protecting. Always carry spare fuses. Fuses come in varying shapes and ratings A 15amp fuse will often protect a circuit which normally carries about 10 amps and give a safety margin of 5 amps, any more than this and the wires may start to cook before the fuse.

Why does the ignition switch have so many wires?
The ignition switch is nothing more than a complicated on/off switch. The main part of the ignition switch simply connects the battery to the rest of the vehicle.
It may sometimes also connect the parking lights and other things, but as long as it switches the battery to the rest of the bike when unlocked and doesn't when locked, then this is all you may need. The rest of the wires may be left unconnected. For small bikes, see also small bike ignition circuits.
To find out what else it does, you will need the manual for that particular bike, as ignition switches differ greatly and get more complicated each year. If in any doubt, see how to repair or modify the ignition switch later.

At this stage there is a supply of electricity from the main battery fuse via the ignition switch to the three fuses. It is now possible to use these three fuses for each circuit.

The Ignition Circuit.

From the fuse chosen for the ignition circuit, a circuit can be built to supply the sparks. This may also include the other engine components such as oil pressure switch and electric starter.
Look at your ignition circuit in the manual or use the nearest diagram from the selection later in this monograph.
Find the coils, they are usually big black or grey lumps with thick wires to the spark plugs. On circuit diagrams, spark plugs are often shown as two thick black arrow heads pointing to each other.
On most bikes, each coil should have one or two thick HT leads to the spark plugs, and one or two ordinary wires. One of these small wires will supply the 12volts from the ignition fuse, (via a simple kill switch if used). The other small wire will go to the points or to the electronic ignition unit.
On some small bikes, there may be only one small wire which is connected to the contact breaker and also splits to connect to the ignition coil and the ignition switch. On small bikes, the ignition switch will short out this circuit to earth when the ignition switch is off, to prevent use.

On bikes with contact breakers there is a wire from each contact breaker to each coil. The wire connected to the contact breaker must be connected to the insulated moving contact spring. This wire must only connect to earth when the points are closed, so check the small plastic insulating washers and the spring mounting are correctly positioned. The condensers (capacitors) will connect between the earth via their mounting screw and to the points wire via the spring mounting nut which holds the small plastic insulating washers and points spring and wire in position. When all is assembled correctly, the wire from the coil will only short to earth when the points are closed.

On electronic ignition bikes there are simply pulser coils (sometimes known as pick-ups) instead of contact breakers. The wires from the pulser going to trigger the electronic ignition unit which shorts the coils to earth. These pulser coils are simple coils of wire around an iron core. As a magnet rotates past, a small current pulse is generated to trigger the ignition box at the correct time. See also two stroke CDI later. Alternatively the core of the pulser coils may be magnetic and a ferrous item passes to interrupt the magnetic field.
There will be either one or two wires from each pulser coil. If just one wire, the other end of the pulser coil connects to earth internally. The pulser wires will connect to the same coloured wire from the electronic ignition box.
Likewise on the electronic ignition box, there will be matched coloured wires connecting to the coils. The other wires from the electronic ignition box will be a 12volt supply and an earth which are usually easy to identify. On an engine with two pulsers, it does not matter which pulser wire goes to which wire, as both pulsers are built the same, and the output for the coils will also be the same, but with different times relative to the crankshaft. Therefore only the correct wires for the pulsers must be decided and likewise the wires for the coils. The only minor problem is to make the coils work correctly for cylinders 1&4 and 2&3 by simply swapping the pulser wires, or the ignition box wires to the coils or simply swap the park plug caps.
If the pulser coils have dual wires, then they may need their individual pairs of wires to be swapped to get their pulses the correct way around.
Cars often use a distributor and therefore only need one pulser, so do not suffer this problem. the problem is getting the right wires from the distributor to the correct spark plugs.
If there are other wires, then they may connect to the tacho, or exhaust valve controller of two strokes, but these will need the manufacturers correct wiring diagram to check.

The 12 volts from the fuse will usually go to the kill switch, then to the ignition coils and also to any electronic ignition box if fitted.
The points will short out the 12 volts in the coil, causing a spark. This is done by creating and collapsing the magnetic field and very high voltage winding in the coil, which must go somewhere, invariably across the spark plug gap causing the spark.

Many earlier contact breaker and pulser systems use mechanical flyweights on an advance retard mechanism to mechanically advance the sparks as the engine revs increase. Later electronic systems use an electronic advance.

The kill switch on larger bikes is a simple on/off switch which if used, must connect 12v to the coils and to the electronic ignition unit only when in the 'run' position. In general use, the kill switch prevents all from being damaged by simply switching off the power to the coils and any electronic ignition box.
During testing, always protect the coils and electronics. Use the kill switch to prevent overheating of the components if the ignition switch is to be kept on, perhaps when testing other circuits. It is best to test each circuit separately using only the fuses as needed, with other fuses being removed for safety.

If fitted, the ignition fuse also supplies power to the fuel pump. A standard solenoid type fuel pump may be supplied with power direct from the fuse or via the kill switch, as it only pumps when the pressure is low. On some racing machines with a motor style fuel pump inside the fuel tank, then this type can be controlled via the kill switch and possibly a tilt switch for safety should the machine crash.
If a fuel injection system is fitted, it should be on its own circuit, supplied via the kill switch.

If the fuel and ignition systems need more current than the kill switch can handle, then all, or at least the fuel pump should be controlled via a relay.
The common type of solenoid fuel pumps use contact breakers inside which can sometimes fuse together and cause damage, therefore it is most prudent to fit yet another fuse, just for the fuel pump and carry a spare set of fuel pump points if touring.

Electric start.

Starter switches differ. Some take the wire from the solenoid to the handlebar starter switch and short it out through the handlebars to earth, but this sort is not recommended. If the wire should short out between the solenoid and the handlebars, then the starter may work when you least expect it, often requiring new crankcases and a trip to hospital.
The safer design has 12v going to the starter button switch then to the solenoid. If the wire should short to earth, then only the fuse will blow, but the starter motor will not work while riding. To find out which type you have, open the starter button switch to see if one side shorts to earth, or whether you have two wires insulated from earth, which means you have the safer type.
The solenoid gives a loud click when it works. Test by connecting the small wires across the battery.
Some solenoids now include the main fuse, a flat strip of steel held by two screws. Therefore this side of the solenoid must connect to the positive, (not the starter motor) side of the battery. From this main fuse will be a wire leading to the ignition switch.
If the solenoid fails, the machine may be started by shorting a spanner across the two large cable studs on the solenoid, shorting out the connections enough to power the starter motor.

As ignition systems become increasingly complex, more components will be added to the ignition circuit, such as a level sensor which will cut the ignition if the bike falls over. If in doubt about the many spurious or dubious components, find out what each does and leave it out of the circuit if not required.
Usually such items are simple switches connected in the circuits to prevent accidents. To prevent the starter working with the clutch out, a simple switch is connected in the starter circuit, preventing use unless the clutch lever is pulled in. Other systems are simply variations on a similar theme. These are not complex, just annoying when there is more to go wrong.

Summary.

The minimum contact breaker ignition circuit is a wire from the ignition switch to supply volts to the coils. Then wires from the coils connect to the contact breakers and condensers.
The minimum electronic ignition circuit is a wire from the ignition switch which supplies the 12volts to the coils and electronic ignition. Wires from the pulsers trigger the electronics box which is connected to the coils.
On small bikes, a single wire goes from the ignition winding (many turns of copper) in the engine, to the points, also to the spark plug coil and to the ignition switch. The ignition switch shorts this wire to earth when in the off position, preventing the engine from running.
A kill switch has many advantages.

To check for a spark, charge up the battery, then lay the spark plugs on the cylinder head and turn the engine over. On electronic ignitions, it may be necessary to kick start or use the electric starter, as there may be a minimum cranking speed for some electronic ignition systems. On contact breaker systems, simply flick the points open and shut. Check for sparks. If no sparks, check the 12 volts supply to each component and also the earth connections. On contact breakers, check for insulated points and spring. On electronic systems look for overheating black boxes and poor connections. Sniff for any burning. See testing later. It all is well, remove the ignition system fuse and prepare to build the lighting circuit.

The Car Ignition Circuit.

The car set up with distributor is simple and an example is shown. It is refreshing to see such a simple design which has worked so well for millions of people for billions of miles.
Find the coil, usually a big canister with a thick wire to the distributor cap, then to the spark plugs. On circuit diagrams, spark plugs are often shown as two thick black arrow heads pointing to each other.

On most basic car systems the coil should have a thick HT lead to the distributor cap and then to the spark plugs, and one or two ordinary wires. One of these small wires will supply the 12volts from the ignition fuse, (via a simple kill switch if used). The other small wire will go to the points or to the electronic ignition unit.

On engines with contact breakers there is a wire from each contact breaker to each coil. Usually one of each, but V6s and larger may have more fun bits.

For points, the wire connected to the contact breaker must be connected to the insulated moving contact spring. This wire must only connect to earth when the points are closed, so check the small plastic insulating washers and the spring mounting are correctly positioned. The condensers (capacitors) will connect between the earth via their mounting screw and to the points wire via the spring mounting nut which holds the small plastic insulating washers and points spring and wire in position. When all is assembled correctly, the wire from the coil will only short to earth when the points are closed.

The other pictures shows motorcycle set-ups. The area of interest is that it can be used in a modern car without the need for a distributor, and two pick ups on the crankshaft position. With this, the coils can be mounted in the cylinder head trough between the cams and make a compact arrangement. This is the way many systems are going with electronics, so you should consider such methods as well as the simpler old set-ups, to keep an open eye on the future. As coils are now very small, some not much bigger then your thumb by using much higher primary voltages from the electronics box, they can now be placed in the spark plug cap, and each coil triggered from the electronics individually rather than via a distributor.

On electronic ignition engines there are simply pulser coils (sometimes known as pick-ups) instead of contact breakers. The wires from the pulser going to trigger the electronic ignition unit which shorts the coils to earth. These pulser coils are simple coils of wire around an iron core. As a magnet rotates past, a small current pulse is generated to trigger the ignition box at the correct time. Alternatively the core of the pulser coils may be magnetic and a ferrous item passes to interrupt the magnetic field.
There will be either one or two wires from each pulser coil. If just one wire, the other end of the pulser coil connects to earth internally. The pulser wires will connect to the same coloured wire from the electronic ignition box.
Likewise on the electronic ignition box, there will be matched coloured wires connecting to the coils. The other wires from the electronic ignition box will be a 12volt supply and an earth which are usually easy to identify. On an engine with two pulsers, it does not matter which pulser wire goes to which wire, as both pulsers are built the same, and the output for the coils will also be the same, but with different times relative to the crankshaft. Therefore only the correct wires for the pulsers must be decided and likewise the wires for the coils. The only minor problem is to make the coils work correctly for cylinders by simply swapping the pulser wires, or the ignition box wires to the coils or simply swap the park plug caps.
If the pulser coils have dual wires, then they may need their individual pairs of wires to be swapped to get their pulses the correct way around.
If there are other wires, then they may connect to the tacho, or exhaust valve controller of two strokes (snow mobile engines), but these will need the manufacturers correct wiring diagram to check.

The 12 volts from the fuse will usually go to the kill switch, then to the ignition coils and also to any electronic ignition box if fitted.
The points will short out the 12 volts in the coil, causing a spark. This is done by creating and collapsing the magnetic field and very high voltage winding in the coil, which must go somewhere, invariably across the spark plug gap causing the spark.

Many earlier contact breaker and pulser systems use mechanical flyweights on an advance retard mechanism to mechanically advance the sparks as the engine revs increase.
Early electronic systems use an electronic advance. This reads the amount of advance to be used according to variables including throttle position, engine revs and amount of vacuum in the inlet manifold. For this reason they are often called a digital 3D map and can be changed for racing purposes, as they are burnt into a chip. A not too dissimilar arrangement is used when employing a digital fuel injection system.

The kill switch is a simple on/off switch which if used, must connect 12v to the coils and to the electronic ignition unit only when in the 'run' position. In general use, the kill switch prevents all from being damaged by simply switching off the power to the coils, any electronic ignition box and the fuel pump.
During testing, always protect the coils and electronics. Use the kill switch to prevent overheating of the components if the ignition switch is to be kept on, perhaps when testing other circuits. It is best to test each circuit separately using only the fuses as needed, with other fuses being removed for safety.

If fitted, the ignition fuse also supplies power to the fuel pump. A standard solenoid type fuel pump may be supplied with power direct from the fuse or via the kill switch, as it only pumps when the pressure is low. On some fuel injected racing machines with a motor style fuel pump inside the fuel tank, then this type can be controlled via the kill switch and possibly a tilt switch for safety should the machine crash.
If a fuel injection system is fitted, it should be on its own circuit, supplied via the kill switch.
If the fuel and ignition systems need more current than the kill switch can handle, then all, or at least the fuel pump should be controlled via a relay.
The common type of solenoid fuel pumps use contact breakers inside which can sometimes fuse together and cause damage, therefore it is most prudent to fit yet another fuse, just for the fuel pump and carry a spare set of fuel pump points.

The Lighting Circuit.

Some ignition switches have the lights switch built into them. This is common on small bikes, where only a main fuse is used. In such circuits, simply use the lights output from the ignition switch to send power to the hi/lo switch and also the tail light and speedo lights.

The high beam warning light is simply a small light connected to the main beam wire.
Speedo and tacho lights are simply small lights connected to the light switch.
The headlight flasher takes 12v from the auxiliary circuit. Not from the lights circuit, but usually from the horn button supply which is very close inside the handlebar switch unit. The headlight flasher can then be used without the lights being switched on, to the flash switch, and from here to the high beam. The headlight flasher switch is usually close to the Hi/Lo switch and may only be a very short wire inside the switch housing to connect to the high beam wire, also inside the handlebar switch housing. See auxiliary circuit.

It is not a good idea to add too many items such as extra lights to the standard lighting circuit, as the ignition switch can only take a limited amount of current. Spot and fog lights should be separately fused on their own circuit from the battery. This way, the main lights are more likely to remain working when needed. Spot and fog lights can be triggered via relays by a connection to the main/dip switch without overloading the main lighting circuit.

The Auxiliary Circuit.

Oil warning light.

Horn.

Brake lights.

Indicators.

For an indicator warning light, use a fully insulated lamp simply connected with one wire to the left indicator wire and the other wire to the right indicator wire. What happens is this: when one side lights up, the intermittent 12v flashes the indicators, and also supplies the warning lamp, the very small current used for the warning lamp is small enough to be earthed through the filaments of the other bulbs. No worries.
Read the info on the flasher unit to see what bulbs it is designed for. Usually 2 X 21W + 5W, which means two 21watt lamps plus a small 5watt indicator lamp.

Fuel gauge and sender.

Water temperature gauge and sender.

Parking light.

There are other items on machines, such as auto indicator switch offs, and other fancy stuff, but these are often more of a waste of time if building your own wiring loom. A simple, reliable wiring loom which does the job is better than an overly complex loom. If fancy bits are required, simply place them on a separate ancillary wiring loom.
Digital speedo and other ancillary items are simply a variation on the above themes, but with a digital interface. See later.

If the original set-up is needed, it is often better to use the manufacturers genuine replacement loom, or to copy the original.

If using or modifying or building alternative handlebar switches but the room for switches is too small, then use small switches to switch a relay. This will allow many of the ultra small switches to be used which can often be carved or moulded into handlebar clamps. Where ordinary electrical switches are used, always use the waterproof version, or employ silicone sealant to waterproof the pivot and any other areas where water will seep in. Alloy coloured silicone sealant makes for easy starter or horn push miniature switches to be moulded directly on the handlebars.

If fitting an internal light to a fitted top box or pannier, then consider quick setting epoxy to glue a micro switch to the case, with the tab bent to release the switch when the cover is removed. This technique can also work for many aftermarket alarms to protect side panels and seats etc.

Checking the wiring loom is simply fitting the appropriate fuses then checking each system by connecting each item in turn, to see if it works are required. Always check the earth connections are well made, including the earths onto the frame so they will not corrode with time. See testing later.

Central locking. Cars think that central locking is a boon. Great until it goes wrong. If the battery dies, then you will need to power up the car from external means. A hidden external 12volt charging socket which supplies directly to one door lock will help you get in ! If you cant get in, you are not going to open the bonnet (hood). A diode may be needed.
Otherwise, simply charge the battery from the socket, but if a major fault has occurred, then this may simply not work. A external 12 volt charging socket will allow the car to be powered up to retain radio and computer data while replacing the battery.

Minimum Tools And Equipment Needed.

For protecting the wiring and connectors, especially for dirt bikes, clear lacquer or clear nail varnish, also silicone maintenance spray and grease. Flexible hair spray will generally protect most wiring and connectors, especially during long term storage.
Penetrating oil for easing tight nuts and bolts in alternators, and switchgear.
If rebuilding switches, then add tweezers and thin, snipe nosed pliers.

Strobe.
A 'strobe' is needed for checking the advance curve and the sparks while the engine is running. This is a powerful lamp which flashes when the spark occurs, causing the internals of a running engine to look as if it is standing still. If too expensive, a timing light is much cheaper but with equivalent lower performance, needing to be used in darker light levels. If preferring to try a simple alternative, a cheap or surplus neon mains warning bulb will do, and can be wired using HT leads directly in the spark plug HT circuit using parts from a broken plug cap. This can be brought close to the timing marks for easier vision. A neon bulb is the small warning light on 240volt kettles and mains sockets which glows red - not exactly brilliant, but very cheap and can do the job for pennies if insulated well.

Four circuits. Charging, Ignition, Lights and Auxiliary. With a fuse for each circuit.
An ignition switch.
Fuse box for four fuses plus spare fuses.
Rectifier / regulator unit.
An electric starter with solenoid.
Two coils to 4 spark plugs from 2 sets of contact breakers or electronic ignition.
A headlight with dip and high beam, tail light with brake light working off a rear brake switch.
Horn.
Indicators.
Standard handlebar switches, containing lights on/off, high/low beam, starter, kill, and horn switches.
The circuit is conventional with negative earth.

Before starting a rewire.
I often rewire a bike from a burnt out wreck, with just a few corroded stubs of wire coming from the crankcase. It you do your homework properly, then this should be an opportunity to do a new, really neat and tidy job.

First of all and wherever possible, get the engine running before removing the old wiring. This reduces the numbers of possible problems to be solved later, such as the electronic ignition, or coils, or ignition switch work etc. This also helps to understand the wiring before removing the old bits. Take this opportunity to see if the battery charges at 14 volts or if there are charging problems.
This may well require taking a few liberties by making a lash-up piece of wiring to check the components.
If the vehicle is burnt out or a wreck, then it may be best to get the engine running first. This is particularly useful before spending money on the rest of the project. The engine can be temporarily wired to run from a fully charged battery, to get just the sparks and starter motor working. This will not need the alternator or charging circuits. Just rig up power to the coils and points or electronic ignition and pulsers, powered direct from a well charged battery. Do not forget the earth connections.
The electric starter motor can be operated direct using the remains of the starter cable or a pair of emergency car jump-starter cables.

Once the engine runs, the rest may be worthy of a rebuild. Start by thoroughly cleaning all components. Where the wires to the alternator are burnt flush, remove the alternator and use new wires soldered to the original connections to the alternator windings. Leave plenty of length on the wires for fitting later. Likewise the pulser units and any other wires in need of repair. Always make sure they are routed safely and neatly.
Switches can be chosen as required, then checked with a multimeter and possibly repaired or even modified.
Other items such as radiator fan and temp switch can be checked while off the machine. Use boiling water to check the temp senders.

If a burnt-out wreck, then also replace the thermostat which has probably burst. The electrics may be damaged, but the internal components fare surprisingly well, even in the worst circumstances. The fuel flames usually consume the carburettor or injectors, but alternators and starter motors always seem to remain usable, but should always be stripped, cleaned and inspected for long term reliability.

Items to bear in mind when designing the wiring.
Checking the parts. Whether you are using non-standard new, or used parts from the bike, the internals must be checked to see how they are wired up internally. Where problems occur, then testing will be needed. This can be done as each stage of the wiring is reached. Three ways are possible; Testing with a multimeter, taking it apart, or reading the original manual. Taking components apart and modifying is covered in section 3.

Once the switches are understood, drawing the wiring diagrams can begin. If parts such as switches, coils, regulator etc, were working all properly before the rewire, then little can go wrong unless they become wet, corroded or broken. See repair later.

If deciding on your own colour scheme, then the following points should be considered. Choose appropriate colours for the different main circuits, with different tracer colours to indicate the parts of the circuit.
For example, if making the lighting circuit white, then you could have a white wire to the light switch, two white wires with red tracer from this switch to the tail light and to the high/low switch. From the high/low switch a white wire with a blue tracer to the high beam and maybe a white wire with yellow tracer for the low beam. This simply mimics the colours used by the lights.
Whatever colours you decide, make them simple to understand and mark them clearly on your wiring diagram.
Wires from the alternator are usually yellow or white.
Charging systems and the main supply to the ignition switch and fuses usually use red as their main colour.
Earth is usually green for Honda, Black for Kawasaki etc.
Keep it standardised where possible, as this will tie up nicely with the unmodified components such as electronic ignition, indicators etc.

Choosing The Wire Size And Connectors.

Make a list of wires required by using the wiring diagram. Decide upon the length needed and by measuring the bike, then add some extra for possible errors in cutting or bad fitting to make life easier. It is common to order to the nearest metre anyway. A typical list is given in Section 3 to act as a guide.

All the connectors that are 'live' when disconnected, must be prevented from making a short circuit. They MUST have shielded sleeves or shielded multipin housings to protect them if accidentally disconnected. So mark them on your wiring diagram and count how many are needed.
Keep standard connectors on the electronic ignition, alternator, rectifier and regulator, so when they need replacing, new parts will fit without problems. If the original connectors are damaged or lost, you can often get some from a breaker, then simply buy new metal connectors to fit inside them.
Multipin connectors have metal inserts which are a little longer than the standard connector, which contain an extra retaining tang to retain the contact in the plastic housing. This is easily bent back enough for careful removal and re-use. Use a straightened paper clip with a flattened end.

Some bike breakers will be only too happy to send you out to the broken bike section with a few tools to scavenge a wiring loom for a few quid. Use this opportunity to salvage any other components that are due to be dumped, such as battery cables, fuse box, broken speedo units to recycle the fuel gauge etc. If the exact bike is not available, the nearest equivalent will often supply most of the required connectors.

Unusual or special connectors can come from old or similar looms. A few uncommon connectors are not available such as some oil pressure switch connectors, so will have to be recycled or made to fit other connections.

The internal metal connectors of multipin block connectors can be replaced where needed, using new pins which come in most shapes and sizes. To decide which ones you need, use a small thin, flattened piece of wire to push back the locking tab on the metal part inside the housing, then pull it out. It is best to try this on an old connector first as it can be fiddly.
If you decide to cut the wiring to a minimum then you can still use standard switches etc, but circuits such as indicators may not be needed.

Designing a Wiring Diagram.

Start with the yellow or white wires from the alternator to the rectifier/regulator unit. See also field coils and sense wire above which may or may not be needed.
Then continue with the 12 volt wire from the regulator to the battery. Usually red. This also goes to the main wire from the battery to the main fuse. The earth wire is usually black or green, to the frame earth.

From the other side of the main fuse, draw a wire to the ignition switch. From the ignition switch when in the 'on' position, back to join to the three other fuses.
The three fuses then supply current to their different circuits as mentioned earlier. Join the parts up using the descriptions given earlier. Ignition circuit for the coils and spark plugs. Then draw in the lights circuit and then the auxiliary circuit.
It will be instantly noticed that spacing is paramount to a neat wiring diagram. After a few attempts, the wires will soon take up a natural 'schematic' arrangement, eventually leading to relative clarity.

Although drawing a wiring loom may seem a chore to many bike builders, it has one major advantage. It enables the wiring to be sorted before the build. By drawing the loom, the way it is assembled and works will be double checked, with any problems sorted well before hassles car raise their heads. It also leaves a permanent record for later when problems may occur.
Another major advantage is that you work out just exactly what it is you are doing, before getting lost in a mess of loose wires and connectors.

Some bikes have the fuse box in the fairing, with the main fuse on the starter solenoid. This will simply require a little repositioning of the items on the wiring diagram.

The earth wires will be the same size as the wires supplying 12v to the component, except the battery earth and starter which must be a little larger.
The starter motor cables can be drawn in a little thicker to the solenoid and the starter motor, plus the thick earth from the crankcase to the battery earth.

Mark in the colours as they are drawn, so each circuit can be easily recognised.

Parking lights are usually connected through the ignition switch, occasionally needing trial and error with a multimeter to find out which wire from the ignition switch will work parking lights. Warning: a diode will be needed, as mentioned earlier. Stay clear of parking lights unless absolutely necessary or consult the workshop manual. The diode is to prevent the power going via the parking light to the lights switch to the fuses, then allowing the rest of the bike to work. See parking lights above. If in doubt, make the parking lights on a completely separate circuit to all other wiring, and connect direct to the battery via a simple switch. Do not connect to other lights.

You should now be able to draw a wiring diagram, or follow a wiring diagram for your bike.
Follow each wire in turn starting from the battery check if they end up in the correct place and colour, and that you know what they do. A selection of basic wiring drawings are available at the end of this text.

Practice fitting each type of connector you will be using, including soldered joints and switches. Test by trying to pull wire off to ensure it's fitted securely.

Some Tips On Custom Rewiring.

There are many ways to cut down on wiring. A popular method on trikes and customs is to use an after-market car ignition switch which has positions for run, run with lights, and starter and then placing it out of sight, often under the seat. This eliminates the need for any separate lighting or starter switches.

If preferred on an enduro, use the indicator switch as a lighting switch, or as a kill switch allowing just one set of wires on the handlebars. Be careful when using an indicator switch as a kill switch on an enduro, use the right for power so if accidentally knocked by your hand, it is more likely to stay on. See also off-road preparation later.

There are three main places to put the numerous connections from the main loom to the handlebars, inside the headlight, under the tank or near the steering head. How these wires are routed is personal preference, but if your headlight is big enough, then design the main loom so that it will go all the way into the headlight, as it's dry and easier to get to. The loom can be routed underneath the bottom fork yoke straight into the headlight, or possibly through a large enough hole in the bottom yoke of a custom show machine.
If a fairing is used, then make the connection just inside the fairing, and easy to get at. This will make the fairing or headlight pod easier to remove.
For cars, under the dash is still the most sensible central wiring area, if access is reasonable.

Where the coils are fitted under the motorcycle seat out of view, then extend the high tension (HT) leads by inserting a strong piece of wire or a small nail with both ends sharpened into the end and adding an extension piece of HT lead, then covering with glue sealant and heatshrink sleeving. On some coils, it is possible to simply unscrew the HT lead from the coil and replace it with a longer one. HT leads can also be routed through the frame if room permits. Some HT leads can be very cleverly disguised or hidden completely. Carefully choose the spark plug caps which will allow the best HT cable routing and style.

The battery should be mounted in rubber to prevent wear against the metal frame, this means some firm rubber foam around the base and sides. A vent pipe to protect your paint from the acid should also be fitted.
The tail light wiring is often found rubbing against the rear wheel, so make sure that you weld or solder small strips of steel or, if using a plastic mudguard, a well glued set of lugs or a tube inside to keep the tail light wires safe and hidden. If using a tube, use staggered bullet connectors on the wiring so they can easily pass through.
Most rear brake light switches deteriorate quickly so use good quality switch, or a type that is cheap and easy to replace.
Always carry spare fuses, as they deteriorate with time. Make sure they are the correct rating. If desperate, use domestic fuse wire across the old blown fuse, again make sure it is of the correct rating, and only use one strand of the fuse wire. In emergency, strip an old piece of wire to remove the copper strands, or aluminium foil, then use just enough to act as the fuse wire. It must be allowed to blow.

What size wires and fuses should be used ?

Lights. Headlight probably 60 Watts, the dip beam usually 55 Watts, even though they are not on at the same time, but if headlight flasher is used = 115 watts. The tail light, 5 Watts. The speedo and tacho lights 2 x 5 Watts=10 Watts, all adding up to a total of 60W + 55W + 5W + 5W + 5W = 130 Watts.
To find the Amps used by this example. Amps = Watts divided by Volts. So for a 12 volt system, the current in amps will be 130 Watts/12 Volts = 10.9 amps. So for the lighting circuit we need at least 10.9 amps, but to allow a safety margin, use a 15 Amp fuse. Do not use a larger fuse than this, as it is the fuse you want to blow, not the wiring.

The circuit supplying the ignition will need to carry enough current for the coils, to be generous, about 5 W, the electronic ignition, maybe 5W, and the starter solenoid supply, about 5W all adding up to a total of 5W + 5W + 5W = 15 Watts. To find the true value, use the multimeter set on the 10 amp rating to see how much current is used.
To find this fuse rating in amps, Amps = Watts/Volts. So for a 12 volt system, the current in amps will be 15 Watts/12 Volts = 1.25 amps. This particular example ignition circuit needs at least 2 amps, but to allow a safety margin use a 5 Amp fuse. Probably a lot less.

The ignition circuit is usually quite small, needing only a 5 amp fuse. If fuel injection is used and/or a fuel pump, then follow the original manufacturers recommended fuse rating. If in doubt, fit increasingly smaller fuses and test until they blow, then choose a fuse rating with a reasonable safety margin. When the machine is up and running, a multimeter set at least 10 amp reading and placed across the empty fuse holder, will certainly eliminate any doubts. Another way is to reduce the fuse rating until it blows. Check it is in maximum load, possibly with the fuel pump and radiator fan working, (if fitted on this circuit). The radiator fan can be run by removing the switch connectors and joining them temporarily.

The auxiliaries circuit will be the horn, about 20 Watt, Brake light, 21W and the indicators, (which are 21W + 21W + 5W = 47W) all adding up to a total of 88 Watts. The fuse rating in amps is: Amps = Watts/Volts, so this is 88 Watts/12 Volts = 7.3 amps. Including a safety margin, use a 10 Amp fuse. If the headlight flasher is on this circuit, add an extra 12v/60W = 5amps. This gives a 15amp fuse for general use.

The main fuse will handle all the above which is 130 W + 15 W + 88W = 233W Amps = Watts / Volts , so this is 233 Watts / 12 Volts = 19.4 amps. so a 25 amp main fuse is used. As not all the items will be on all the time, a 20 Amp fuse may do for initial testing and just to be on the safe side while testing. Later this can be replaced with a 25 amp fuse, should it blow.

Find out the wattage of your own components and follow the above example using your own numbers. If your numbers differ widely then check again. A good quality multimeter which can measure the current up to about 10Amps will allow assessment of each individual component or the more unusual items if in doubt.

Making, Checking and Fitting the Loom.

Where one wire goes to several places, such as the indictor switch to the front and rear indicators and the indicator light, then it will be necessary to solder wires together. This is best done where the wires are naturally split to go their separate ways, such as the indicator wire going from the handlebar switch into the main loom. These can be soldered to two wires to front and rear indicators. The indicator lamp connection would be soldered to the front wire closer to the lamp, usually where it uses a connector inside the headlight shell.
The same for ignition, where the wire splits to feed the coils and electronic ignition and perhaps the fuel pump.
Soldering the joins will mean stripping back the wire and twisting a number of separate wires together, then allowing solder to flow between all the strands for a secure connection. This should then be cleaned free of any flux and covered with tape or heat shrink. For best results, use heatshrink with an integral sealant which excludes any chance of moisture attacking the joint.

The crimping of connectors is mentioned elsewhere. Always try to use connectors similar to the original or of better quality. Gold plating is of dubious use in a harsh environment, as simple maintenance spray with a waxy film is more likely to penetrate and prevent corrosion of the copper wiring inside the insulation, were much of the corrosion occurs, not on the connectors, be they gold plated or not.

Where the ends of the loom connect to various items, there will be one, two or more wires connecting a single wire in the loom. The front indicator wire will have a double connector, to take the indicator and the indicator warning lamp connections. The ignition wire and auxiliary supply wires at the end of the loom where it enters the headlight, are often given a spare connection for later modifications. This is also done to the supply under the seat, allowing an anti theft device, or camping light to be supplied from the main fuse, or from another separate emergency fuse.

To improve flexibility around the steering head, it is useful to have the wires gently twisted inside the loom like a rope, so that flexing is more easily accommodated without undue bunching or kinking of the wires. If these wires are in a protective sleeve, then lubricate them with a little silicone grease to prevent undue wear of their plastic insulation. This is particularly important on bikes such as enduros which have a large degree of movement and high levels of stress on these wires. In extreme cases, consider routing the wires near the headstock to run vertically for a short distance to minimise problems of flexing.
As the wiring passing the steering head is a common area for vandalism, then consider sliding a sleeve of wire netting, similar to the Chinese finger trap over this area. This will help prevent it being cut through with a knife. Such sleeving is available as copper, or preferably steel shielding on larger cables, or can be wound over the loom by hand deconstructing old throttle cable inners, before fitting the outer plastic sleeve.

In some case, there may be the need to add some redundancy into the wiring loom, such as the ability to add indicators to an enduro bike at a later date. Where necessary, it is very simple to add a few more full length wires to a loom. These should be left with their ends looped and tucked back into the loom, showing just a part of the wire, which can be coaxed out later if needed. Always tuck a good length of spare wire back into the loom, so that almost anything can be fitted. This also allows for a broken wire to be bypassed with an alternative emergency wire should a fault occur in the future.

Where needed, a set of looms can be built. Perhaps a basic loom, plus a separate loom for a fuel injection system, and perhaps a separate loom for spot and fog lights. Separate looms make maintenance much easier. Separate looms are not common on commercial machines due to cost.
For those who tour, it is often useful for an external connection for a tent light, air pump or other items. This should be a separate loom with its own fuse, allowing it to be connected from under the side panel etc, or unwound as required. Where this is fitted directly to the battery via a fuse, it can also be used to charge the battery with a battery charger at home.

Do not connect the battery yet.
Following the descriptions of each circuit as mentioned earlier, work though each circuit from battery, main fuse, ignition switch, individual circuit fuse, to switch to component etc. Do not forget the earth connections.
With everything placed where it belongs, lay the wires along the frame as intended, 'tailoring' the wires then fitting the connectors as you work through each circuit. First fit the wires to the connectors for the standard switches and other electrical components such as rectifier/regulator etc.
It is far easier to fit the reconditioned alternator with three new, long yellow wires to the bike, then to route and clip them in position along the engine and frame towards the rectifier/regulator before fitting the plastic sleeving and finally the connectors with perfect placement.

Tailoring the wiring on the bike to match the original fittings will ensure compatibility with commercial replacements. Check that the wires will not be stretched when the steering is at full movement left or right. Any wires that will go through braided nylon sleeving will probably have to be threaded through this before fitting the connectors. Always cut the wire a little longer to be on the safe side, and make sure any insulation sleeving is fitted before the crimping is done.
If wiring direct to the switches with solder joints for minimal full length wiring, as common on customs, then always work the lengths back from the fitted handlebar switches. Ensuring the full length wires can be removed through the frame. These usually all end up under the seat in the electrical box, in the headlight shell or under the tank.
Once all the wires are in place, lay them together neatly and tape them every few inches and wherever the loom splits into two or more directions. Check the way the loom follows the frame and adjust if needed. It is important to be able to place the wiring in clips or other restraints, as a flexing loom is a problem loom.
Where the loom passes the steering head, it is best to either cover with a long length of split flexible tubing, or braided nylon sleeving to protect from any wear caused by flexing. Around the steering head, the wires should be slightly twisted like a simple rope, to prevent the wires from kinking when flexed. Unless for show, do not platt the wires, as Platting makes it impossible to use an old wire to pull a new wire into place in the loom, should one need replacing.

Finally disconnect all connectors, except the earth wires which should all be connected. Check all the earth wires between points on the frame, to the head and tail lights, to the electronic ignition unit, indicators etc. Earth wires must make a good electrical contact with the frame bolt or other fixing, remove paint if needed, then protect with grease.
For carbon motorcycles with advanced wiring, there are other options under study. See later monographs or updates.

As the wiring loom is not yet covered with tape, it is still possible to make last minute changes.

Checking The Wiring Before Use.

Starting at the fully charged battery, connect the main fuse. Connect the bulb and croc clip to the return from the ignition switch to the three fuses, it should light only when the ignition switch is on. Check the ignition switch in all positions. Then insert each fuse to check each circuit in turn, again using a simple bulb or multimeter.

Connect up the kill switch and connect the croc clip between the coil connectors and earth, if the bulb lights, when the kill switch is in the 'run' position then the kill switch works. Test power goes to the electronic ignition connector in the same way. Do not connect an expensive electronic ignition unit until the kills switch works correctly. Check the bulb goes out when the kill switch is off. Fit the electronic ignition components then the engine can be cranked over to check for sparks. If a strobe is available, then the ignition timing can also be initially checked. This can be done using the kick-starter or with jump leads onto the starter motor.
Likewise check the lighting and auxiliary circuits in a similar manner.

Give the switches many on and off cycles to check they work reliably, as they may work after standing for a year, but may fail quite quickly if dirt or corrosion has occurred during storage. Work your way through until any fault is found. When any part fails to work, remove the fuses to the other circuits, then safely work on just the one circuit at a time.
If problems occur, then work back and forwards along the wire to the problem. Use a simple bulb with two wires and croc clips. Connect one croc clip to the negative side of the battery, the other croc clip to the main fuse holder. If the bulb lights up then all is OK so far, then work towards the fault, reconnecting each item as required.
When problems occur, check the earth return wires to frame and the battery are making good connections. Connect the bulb between the battery positive and the earth wires to check the earth connections to the frame. Work though logically until sorted.
The charging and ignition circuits can only be checked against the wiring diagram at this stage, double check that the are correct according to the diagram and that you know how they work.

If confident, disconnect all other fuses and only connect the ignition circuit, then switch on the ignition switch and put the kill switch to run. Then check the electronic ignition for excessive heat, use a finger and also sniff for burning smells.
If the engine turns over you can check for a spark at the plugs, although when using a less than fully charged battery for starting, the spark may be weak.
If you have points then you can check for a spark at the plugs simply by opening and closing the points manually or with a screwdriver across the open points, and watching for a spark. Adjust the ignition timing so the points just open at the F mark.
Once the sparks work, use the kill switch to prevent damage to the coils and electronic ignition box.
The charging circuit can now be connected. The alternator, rectifier / regulator and any field coil or sensor wires.

Checking The Whole System Under Working Conditions.

On smaller bikes with just one alternator wire to the diode leading to the battery, check for AC between this wire and earth, such as the crankcase. On 6volt systems, the battery voltage should rise to 7.5 volts while running.

What Can Go Wrong.

It is possible to get parts mixed up and put a six magnet rotor on a four pole stator or vice versa, so always keep the rotor and stator as matched pairs unless you can feel the magnets and count up to six.

If a totally different electronic ignition box is used, then check the ignition timing with a strobe, as the pulser coils may be wired back to front, requiring the pulser wires to be swapped to give a N-S instead of a S-N magnetic pulse.
Refill the float bowls and try again. When running, check the battery charging again.

Wiring problems are mainly due to the wrong connection of wires, so the use of an easy to follow colour scheme is important. The problems can be divided into various types, no electricity, where parts don't work, too much electricity where bulbs blow or parts get hot or melt, or intermittent, where parts fail only occasionally.
Fuses will prevent most problems from getting worse. Unfortunately this can lead to the cost of using too many fuses, especially if an old loom has been poorly repaired. For cheap testing fuses, it is best to strip some spare wire then use an appropriate number of strands to mimic the fuse until all is well. A few strands will often do, and can be placed across the fuse fitting, jammed in position by a blown fuse. This will still do the job, saving a lot of cost if problems persist.

No electricity is due to either an open circuit where the circuit to the battery or to the earth is broken. Check this using the bulb with crocodile clips, one clip to earth and the other clip connected to the circuit at each join in the circuit. Start from the battery, working through the circuit until the test bulb doesn't glow, the fault is between this and the last connection. All too often a broken or corroded wire, a corroded switch or connector, or a bad earth on the mounting bolt.
All earth connections should make electrical contact. If fresh paint is applied, scrape off for a good electrical contact, and use a little grease to protect from rust.

Too much electricity with the engine running will be due to the excessive voltage caused by a damaged, or possibly partially connected or unconnected regulator, so check for correct connections to the unit and to the alternator. Some regulators may have a sense wire (see above and later) connected to the auxiliary or ignition circuit and if it is not connected, then it cannot tell the voltage on the bike and so cannot regulate it.

If components blow without the engine running then they must be the wrong voltage such as 6v bulbs on a 12v system, or have delicate internals such as electronic ignition units which have been wrongly connected. Be aware for burning smells and hit the kill switch. In some cases, double check if the fuse has a larger rating in amps than it should have.

Intermittent faults are difficult to find, so when they happen, take careful note of what the bike is doing when it occurs, such as rain, or only when the handlebars are turned one way, over a bump in the road etc. From this information you will have to decide what is causing the problem and then try to reproduce it by moving/shaking/stretching the wiring while looking for the fault to appear.

On rebuilt looms, look out for loose or corroded connections, or if the loom is old, then suspect any soldered joins inside the loom where poor soldering can cause the wires to part. This can happen even in bikes only a few years old.
If problems are time dependant such as failing after a few minutes, then suspect worn points or condenser, poor contacts, corroded or poorly made connectors, overheating or tired electronics.

When charging correctly, then reconnect the circuits one by one and then test as if riding. Run the engine and turn the handlebars fully, bounce up and down on the seat to see if any parts underneath rub or any other problems occur. If it's a dirt bike, waterproof the connections fully, then hose the bike with water while running. Then dry the loom fully and again waterproof the connections fully before taping up. Spray silicone spray into each connector, wipe any excess off, then seal the connectors with silicone sealant or bathroom sealant where the wires enter the connector, then spray the connected items with hair lacquer.

If all is well, the loom can be taped up fully. Start at the ends nearest the connectors and tape over any plastic sleeving so that it wraps tight about the wiring. Finally tuck in any ill fitting wires and tape up the centre section.
Main areas of long term concern are the tail light wire rubbing against the tyre, the main loom around steering head, and water getting into any soldered joins deep in the loom. Tape up the loom so water cannot get inside, to reduce possible corrosion and failure at a later date.

When riding for the first few hundred miles, carry a set of spares and tools.

Wire sizes for safe current loads. For normal use on motorcycles you need only use four sizes of wire, a special starter cable, High tension leads (HT) for the coils to the spark-plugs, 17 amp wires or larger, depending upon the bike, for the main battery and ignition switch to fuses and if you are using a lot of extra electrical parts such as fog lights etc. Also 8.7 amp wire for the rest. Approximate numbers will do.
The following gives details of the normal wires used in vehicles and the safe loads they can carry in amps.
The first number is the number of strands of copper in the centre. The second number is the diameter of each strand, the third number is the total cross sectional area of the copper strands in mm squared, and finally the current it can safely carry in amps.
Commonly used wires are:

9 / 0.30 , 0.65mm sq , 5.75 Amps
14 / 0.30 , 1.00mm sq , 8.75 Amps
28 / 0.30 , 2.00mm sq , 17.5 Amps