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[Barry_Q]

The tacho on my Lightening has a fault. Well, it's not the tacho itself. It's the wiring loom. There's a break in one of the wires. I can turn the handlebars to the left and the tacho works. Turn them anywhere else, the tacho stops. Finding a break in a wire is tricky at the best of times. However, it's made even harder when the wiring diagram I have is too small to see clearly (Photocopied handbook). Does anyone know where I can get my hands on a decent diagram?

[jefrs]

There are a couple of diagrams by Scalyback on here if you search. The ones I've seen do not show a tacho, although I have fitted a tacho to my C5. Perhaps easiest way to find the break is to replace the offending wire entirely and run it on top of the loom. The loom should be almost vertical at the headstock so it twists rather than pulls, not always easy to arrange. There is a wiring diagram in the Workshop Manual but the PDF I have is for C5, B5 and G5.. The Smiths tacho needs a power supply +ve and gnd, an illumination supply from pilot lighting, and a wire to the coil.

[Barry_Q]

The biggest problem is finding the offending wire. No wire has actually snapped. Another problem is that the 'signal' wire from the coil has more than one function. It Earths out the ignition at the Ignition switch. It acts as the cut out wire at the handlebar kill switch. It also provides the pulse to the tacho. So I know that wire is fine in the main loom. The Ignition switch sub-loom is OK. The kill switch sub-loom is OK as well. The fault may lie in the spur that goes to the tacho. The tacho lights are on a separate sub-loom, so they're OK. The fuel gauge works fine as well. I'm sure that the fault is inside the headlight somewhere. I'll find it!

[Colin F]

My understanding with the Lightning is the Tacho takes a pulse off the alternator,yellow wire that goes up to the AC lighting regulator.
Colin

[jefrs]

The contents of the headlamp are a complete mares nest, I know the problem. You do have a broken wire but it is making intermittent contact. The break will be where the loom goes around the steering head but the insulation will show no sign of the break. The loom there should be vertical so it does not stretch but twists and turns when you turn the bars, not always easy to arrange; this is the cause. You need to trace the wires from the tacho back down the loom, opening it up, past where it disappears under the tank, and where in doubt cut out and replace all those wires to the tacho. Check all the wire insulation in the loom for cracking and where you cut into the wires inspect them for black or green corrosion of the copper. Hate to say it but it may be indication of further wiring problems. A lot of folks are scared of wiring when they shouldn't be, it looks complicated but it you do one wire at a time it's not.