Motorcycle Repair: Honda CB125 1976, honda cb125, wiringdiagrams

Question
my bike wouldn't start. was running great 2 hrs previous.  found out it was a fuse stored by the battery on the left side.  had already placed a new battery in before discovering it was a fuse.  day or two later i discovered at night the head light wasn't on.  flipped the brights on, and it worked for all of 3 seconds before going out.  tail light won't work either.  turn signals do work.  had put a new headlight on last year.  bike is running great aside from all that.  whats the deal w the head and tail lights?

Answer
Nathan, having a fully charged, load tested battery is key to keeping the electrical system in top shape.

It sounds like the rectifier may be damaged now, but something allowed the alternator output to go beyond 12v and blow out your headlight and tail light filaments. Carefully inspect all the wiring connections inside the headlight shell, to be sure that all colors are matching up with each other. Switching a black with a black/white tracer wire would cause problems, for instance.

I think you will have to buy new bulbs and then test the headlight wiring connections with a volt meter before you plug the bulb back in again. The 1975-onwards bikes have auto-ON headlights, which run directly off the charging system via the yellow wire. That wire is unregulated. Be sure that the ground connection for the headlight bulb is clean, tight and secured to the connector.

http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class  see 1976 CB125 diagram for details.

Bill Silver