Motorcycle Voltmeter

Back in the good old days motorcycles were fitted with an ammeter to allow you to check your charging, these days of course cost has ruled this out. This can be a problem as not all systems are as reliable as they could be. If your voltage regulator blows this can create a lot of expensive repairs, as it can kill the electronic components on a modern bike. To solve this I've fitted a voltmeter. A healthy system should maintain 13.5-14.5 volts with the engine running, anything greater than this will show the impending failure of the regulator.

Components:

Voltmeter, this is a panel mount type.

Wire.

Heat shrink tubing.

Terry clips, to make the mounting.

M4x10mm screw and nut.

Assorted connectors.

Tools:

Multimeter.

Connector crimping pliers.

To make the mount I used two terry clips held together with the M4 screw and nut as shown. The size of clip depends on the size of your handlebars and meter. For most bikes a 19mm clip will fit a 22mm bar, the meter has a 25mm clip.

Push the meter into the larger of the clips, and tighten the nut to fix tightly.

Cut two pieces of wire, it's best to over estimate the length needed, this can be trimmed later. Pass these wires through the heat shrink tubing.

Using a heat source ( in my case a low flame on the cooker! A heat gun is better if you've got one.) shrink the tubing to create a neat loom.

Strip the ends of the wires and crimp on a 1/4" spade terminal to each.

Push these onto the terminals on the rear of the voltmeter, noting which is the positive (+) and which is the minus (-).

The voltmeter has to be connected to the motorcycles wiring loom, to do this I decided to create a "tail". Two in fact, one for the supply in and one to earth (ground).

Using a short piece of the wire, connect a female type connector to one end. The type I'm using is a three way outlet. This will allow me to fit other accessories more easily in the future.

First remove the headlight reflector, so you can access the wiring loom.

Push the voltmeter onto the handle bars, in a position to suit yourself, and feed the meters loom through the back of the headlight shell.

Now comes the difficult part. You need to find a switched, fused, positive supply, and a negative earthing (grounding) point.

The first place to look is the wiring diagram. Unfortunately as each motorcycle has a different scheme I can only offer guidelines. Check the fuse box in the diagram and decide which is the outlet side. The input wiring is usually all the same colour, the outputs are different. Pick a colour, (it may have a second colour trace).

With the ignition off push the positive probe of your multimeter into a connector block in the headlamp with the matching wiring colour you have chosen from the wiring diagram. Earth (ground) the negative probe against the frame. The meter should read zero. Turn the ignition on. You should get a reading of around 12 volts if you've picked the correct wire.

The earth (ground) wire is usually easier to find, look at the battery symbol on the wiring diagram, the colour of the negative side is the one your looking for.

First, using a Scotchlock connector crimp the positive tail into the power supply, do the same to the earth (ground) wire. A Scotchlock connector allows you to tap a wires electricity without cutting the wire.

You can now strip the ends of the voltmeter wire and make a temporary connection. Switch the ignition on and check that the voltmeter works.

If it does, check that all the other electrical items also still work (horn, lights etc.).

If it doesn't check that your temporary connection is good, that you've connected the volt meter the correct way round, and that you have got the earth (ground) wire.

If every thing is ok, you can now trim the wires to length, add connectors, and connect up.

Check every thing is still working, and refit the headlight reflector.

If every thing is connected properly when the ignition is turned on the meter will flash all zeros and then read the voltage in the wiring loom, usually around 12 volts. Pressing the starter button will show a drop to around 10 volts momentarily, and then rise to 13-14 volts as power comes from the generator. On revving the engine it should not exceed 14.5 volts. Any more will show that the voltage regulator is faulty, and needs replacement.