Where have the volts gone?

Some simple tips to improve lights and ignition.

Ignition and lighting systems can often be improved considerably by a very simple low tech modification which can be done by almost anybody.  This is generally applicable to systems old and new, with points or electronic.  Before reaching its destination the current from the battery has to negotiate many obstacles which result in the reduction of this current, in other words the voltage across a particular component will be somewhat less than the voltage at the battery.  This voltage drop can cause significant reductions in the performance of some functions. This hindrance to the free flow of current is known as electrical resistance and has many sources, for our purposes the main ones being ;---- connections, the wiring itself and probably the worst offender is switch contacts. The ignition circuit usually has at least two sets of contacts to negotiate, viz; the ignition switch and the kill button.

The headlights may have three sets, --- the ignition switch, the lights-on switch and then the dip switch, so it's little wonder that I have often measured voltage drops of 2 to 3 volts leading to these items.  This represents a drop of 15/23% of the battery working voltage of about 13V.  That can sound bad enough but the energy in the spark or the power of the lights depends on the square of the voltage getting to them.  So on that basis the above voltage drops mean a reduction in performance of these systems of 28 to 41%.  No wonder that some people find it necessary to fit higher wattage bulbs and expensive high performance coils.

We cannot eliminate all of this loss, but by using thick enough wire, few connections and good quality relays the loss can be reduced markedly, the voltage drop across good relay contacts will normally be much less than across the puny contacts in the handle bar switch gear, particularly after being exposed to the rigours of damp weather.  The diagrams show the differences required in the light and ignition circuits to incorporate the relays.  A slight complication but in many cases the performance benefits compensate, you may even get better results than buying expensive coils, although of course the pose value is inferior.  After all, a single pole. 30A. contact rated 12V. coil relay is much less sexy than the latest high tech flame throwers, even though it may work better.


The lights on my car had always been particularly poor, it’s a Fiat and we all know about Italian wiring don’t we?  A few months ago I measured the voltage drop en route to the lights, I can’t remember the actual figure but it was the highest that I’d ever encountered, not surprising because the cables were also the thinnest that I’d ever seen for lighting duties.  I mounted two good relays near the lights and fed them with some nice thick cable direct from the battery.  The difference was amazing, my wife thought that I’d gone out and bought new lights, but then she thinks that a relay is a race with multiple runners exchanging sticks.

If the manufacturers of your bike have done a good job then you won’t benefit from similar modifications, because they only overcome basic deficiencies, however it’s been my experience that most machines are not good in this aspect and can be improved quite easily.  If you or a friend have a voltmeter you can check things out first, just measure the voltage drop directly from the battery terminal and the coils or light bulb.  If it’s more than about half a volt then think about adding a good quality relay, they’re very cheap in car accessory shops, and maybe thicker wire to feed it.