Weird Electrickery

[MellowYellow]

Pal of mine has restored (from a pretty ropey state) a '72 Honda 350 twin. He knows what he is about and is pretty good with electrics.
Bike is now on the road, and other than some crap in the petrol system it goes very well.

PROBLEM : -

Indicators work with ignition on but engine not started.

They don't when the engine is running.

Help preeeeshiated folks.

[Ruffian]

Do you have a wiring diagram for the bike?
Has it been cut about at all??

[podrick]

He may have used a positive as a negative, many switched positives become negatives when 'off'
If that is the case he would have positive and both sides of the circuit therefore no return circuit.
Hope that makes sense ??

[Jug]

Can't be that as the only thing that has changed, between ignition On and engine running, is the voltage in the loom.

I would look for bad earths.
Look at the voltage drop difference across the indicator circuits when working and when engine running.
Can't be more specific about where to test without seeing a circuit diagram.

[MellowYellow]

[MikeZ]

What about the horn. If that is the same then problem is before that junction. If horn ok then problem after that junction. But often with d stuff it is the ignition switch contacts are worn, try a different ignition switch, i have a good one lying around you could borrow if u like, but best bet is to strip and examine and clean up contacts inside switch, they're pretty easy to work on.

[MikeZ]

Sorry typo: "With old stuff"

[Mervin]

Cherck the wattage required for the bulbs the 70, s Yamaha RD,s will only work with 27w bulbs using the original flasher unit

[Jug]

I'll have a proper look tomorrow when I'm back on my PC but for now I'd think it's likely a regulator or rectifier issue. Has the voltage level been tested when the engine is running?

[MellowYellow]

Thanks for all that.

Will pass on the wisdom later. Chap is 76 and not in the best of health, so isn't compos mentis until a bit later on.