Motorcycle Repair: tail light, honda cb 350, wiringdiagrams

Question
Bill - I have a 1969 Honda CB 350 ( I bought it in 1970). I renovated it over the last two years and have one thing left to fix. The tail light will not go on when I depress the foot pedal, the hand brake works just great. I replaced the switch with no help and even shorted around the switch to no help. If I run a power line from the battery to the green/yellow line the light works. The headlight hi beam indicator won't work also. Suspect the regulator might be the problem but have no idea why.Can you help getting this old favorite up and running>
Thanks
John

Answer
John, Check the wiring diagram here:  http://oldmanhonda.com/MC/WiringDiagrams/MCwiring.php#class

Use a 12v test light to probe into the brake switch on the black wire (switched hot) and then check the green/yellow wire side while depressing the brake pedal. You may not have it adjusted fully so that the plunger is making the connection internally for the switch.

I would also check the tail light socket to see that the ground path is all intact. Honda used a fine braided wire from the socket base to the mounting plate, which eventually makes a ground connection. If you have an open ground, the brake light will try to go back through the tail light wiring electrical path and you get a funny dimmed light at the back.

If your high beam is working at the headlight, then check the condition of the indicator bulb first, then the connection at the high beam wiring inside the headlight, as well as the ground to the rim and headlight shell.

A 12v test light will help you follow the voltage paths, but be mindful of open grounds, as well.

The charging system has nothing to do with this problem unless the battery voltage is dropping down into the 10v range.

Bill Silver