Boxerworks.com

Hi All

Rear brake activation reliably triggers the stop/brake light, the front brake is intermittent to not triggering at all. The wiring from the below tank master cylinder triggers the light when shorting the contacts which makes me think the loom is ok, although I replaced some shonky wiring by the PO with soldered joints new connections and suspected the brake switch from the master cylinder. The bike has an S fairing conversion carried out by the PO and as mentioned there were a number of dubious wiring hacks up front where cables had been simply twisted together and taped...

Noticed today when tinkering that the front brake switch works reliably with the headlight off and will activate maybe once with the headlight on but not in subsequent uses.

Other quirks of the electrics I've noticed are the speed of the indicators can vary and also the voltmeter needle will waggle wildly when activating the indicators.

I had an old 1980 Vespa with a bad earth which would affect indicators - is the earth likely to be the issue or do I need to look somewhere else?

I've a Haynes manual with the wiring diagrams, a multimeter and a little time, but would be delighted to not have to radically tear into the loom, disabling the bike in the process...

Where would I start?

Cheers

Ade

Sounds like your having ‘bad ground’ issues.
Not being there in person to evaluate the situation, here are a few things I would suggest you try to zero in on the cause of the problems you are experiencing. Keep in mind that (factory) ground wires on your bike are BROWN.
Individually check that all the brown wires for all these components have (near) 0 resistance to ground (battery negative) with a ohmmeter.
headlight bulb
voltmeter
4 turn signal bulbs
stop light bulb
You might find the problem right away, like a corroded terminal or damaged wire.
While you’re at it, check any other brown wires you can see, in the headlight shell, along the main frame, etc.

A bad reading is an obvious ground fault, but keep in mind that while the ohmmeter test proves that you have a good ground with no load, it doesn’t guarantee that the ground will be good with a load.

You can temporarily hotwire any suspicious brown wire that you come across directly to the battery negative to see if that fixes things.

Thanks GSPD, will have a look over the next week.