Which amperage wires to use?

[j.wilson]

Cables are generally limited by “volt dropâ€￾- impurity/characteristics of the copper in the cable that resist the flow of electricity.

Volts in one end don’t come out the other.

Some of the electricity that is put into one end turns into heat before it reaches the other end. This heat will even melt the insulation from around the cable (and solder).

It’s not quite as easy as “5 amp cableâ€￾.

All copper is not a perfect conductor- all cables get warm to some degree.

The aim is to use the smallest cable where that temperature increase is within acceptable limits.

Motor cycle cable is “multi strandâ€￾ because it is more flexible and suffers less from vibration damage.

Single core cable like door bell cable, or household wiring cable is not suitable. Also, just because speaker cable is multi strand does not make it better- in this case it is very prone to corrosion.

Stick with purpose built vehicle wiring cable.

The longer the cable the more loss (of volts) will occur, the more power that you require it to flow the more loss (of volts) will occur.

Both of these mean the power available will be less and the cable will get warm.

Physical insulation will also prevent the natural passage of heat from the cable- a bundle of cables will get hotter than a single cable.

Of course, often the equipment may not continually use power and so the cable can be under rated- because it will only be used in short bursts and gets time to cool down(the horn springs to mind).

It’s not a bad start to simply count the threads within the existing cable and measure the diameter of each thread. You can usually identify the cable then- simply extend like with like.

Unless you have had a problem.

Most people worry about the high tech “electricâ€￾ side of the cable when failure usually occurs through abrasion, over heat (due to a short), over heat due to touching hot things like exhaust, failure of cables due to vibration, failure of connectors (or the crimp to the connector) and finally corrosion.

If you have a problem, you might want to do something specific to make sure this does not happen again.

If you always have a problem with your wiring fixes and so hate electrics- try getting some new equipment to improve your results- DON’T GIVE UP, it’s not rocket science and well within the average person’s capability- it’s just equipment and experience.

So:

Keep the cables away from the exhaust and away from things to chafe on.

Always use suitable fuses- they are only there to protect the wiring.

Always encourage cable vibration and movement to occur over as long a length as possible. Cable runs around the headstock for example should not be cable tied so that the steering twist occurs over a couple of inches of cable- they will work harden. So too for vibration, spread the impact- remember when you clamp the cable to the bike you are preventing movement not vibration, you are probably clamping the cable to the very thing that is causing the vibration.

Most of the concern over solder joints in cable is a mechanical one- stranded cable is flexible and resists work hardening, BUT when you solder it the cable becomes rigid; specifically the vibration is focussed on the points where the solder ends- so it’s always good practice to cover soldered joints with heat shrink so that bending can’t occur immediately where the joint ends. Don’t make the heat shrink too rigid, the aim is to spread the vibration over a length of wire not to simply shift it to a new point.

Solder joints are not prohibited, but can be less reliable if precautions are not taken. I'm assuming here that your solder joints are pretty good quality and not dry- or over heated with the solder left in spikes, or strands of wire stick out the joint in all directions, and you didn't use bakers fluid as a flux "because it's really good".

Corrosion. Copper is very susceptible to oxidisation- and so are the metals in solder, this is not helped if there is any residue of solder flux remaining on the joint- so soldering has a further caution- make sure you clean off flux.

Road salt is another great source of cable failure- especially at connection points.

Finally, connections.

Always use a good stripper for the insulation (there must not even be a nick left on the copper surface as this is where stress cracks start) and a suitable crimp tool.
Making good connections is surprisingly easy with the right tools, and should look pretty identical to the factory results.

There was a time when good tools were £80 and hard to justify, but now they are £15- no excuse not to have one. Avoid the cheap tools and connectors that were popular when the proper tools were very expensive (pre insulated just “squeeze-em-upâ€￾ types or the clip-on cable cutting connections).

Protect the connectors from water ingress and support them. Consider vibration and corrosion to be your biggest advisories, equipment and workmanship your defence against them.

In short, when adding a bit of wire to the loom, fit something no smaller than what is on it, make sure the joint is crimped properly (quality stripper, connector and tool) and protected from vibration and corrosion.

Try not to bury the connections/splices in the loom (you will always worry about them) make sure they are accessible for inspection. All will be fine.

VWP are a great source of small lengths of different grades of wire, available in a very wide range of colours- as well as heat shrink and tools.

Finally, I have had several bikes that had wiring problems from the factory- joints in the loom, incorrect earthing/connection points, trapped insulation, large volt drops, etc etc.

There is no magic world out there where everything is perfect- although older Italian bikes are electrically pretty good as pretty much everything has failed and been replaced with good stuff at some point.