Topic: quick q... electrical gremlin.

[domer]

here is a weird one. 73 cb500, 1 fuse, headlight switch has off position... so out of the blue, with the headlight on, the tail and brake light dont work, with headlight off the brake light works, nothing in park. bulb is new... i havent tested a damn thing as im at work... seems to me the bike is trying to tell me something. but what?
no other issues to speak of, blinkers work, headlight works (high beam has always been dead, but i dont ride at night) battery is good and she runs ok. just thought id ask since im getting paid to sit here and do nothing... thanks

[domer]

o.k. maybe i can get some help this time... i tested everything, bulb is good (tested and tried it in my truck) i have 11.9 volts in the socket for tail and brake and tested using the inside of the socket as ground (mimicking the light). but when i insert the bulb... nothing. still have power going to it but no light. here is the kicker, when i turn off the headlight, the brake light works... but when i turn on the headlight nothing, no brake no tail?
help? if i scratch my head anymore im not going to have any hair left!!!

[TwoTired]

Two suggestions.

1 - The bulb socket power pins are spring loaded.  Sometimes they fail or there is tension on the wires to them that compress the springs out of contact with the bulb terminals.

2- check for broken/absent grounds or connections with the Green wire distribution buss.

Does the bike still have stock wiring?

[domer]

stock wiring for the most part, and the socket passed all continuity tests i put it through ( tail to ground / brake to ground all with the bulb in) its an old lucas style light that just has case ground, no wire., i did pull the spring loaded base out of the socket, wires are good, cleaned the contact points for #$%*s and giggles same results. whats got me going crazy is the brake light working just fine with the headlight off. guess im just gonna have to replace the tail light assembly?... but that doesnt fix my confusion...