I had a problem with the main beam warning and indicator warning lights on the handlebar display. It turned out to be where all the earth wires joined inside the headlamp. 40-odd year old bullet connectors were quire heavily tarnished meaning that the earth current tracked through whatever route possible. Our bikes might be old, but at least we can access all the individual wires and connections, and with a little patience they clean up quite well. The other similar problem I had, which caused a lot of head scratching, was the main fuse failing quite often. It turned out to be the multi connector behind the fuse carrier, upon unplugging it all the connections inside it were a nice green colour!! Apparently if a fuse "blows" in the middle of the glass then it's a short circuit, but in my case the end caps of the fuse were falling off through overheating, caused by current having difficulty being drawn through the poor connection. 30 minutes work with a set of jewellers' files cured it. Be lucky. Mike.