Tailight Problem

[Bobalouie]

I am having a problem with my taillights. When I have my headlights on, and I hit the brake, the drivers side goes completely out. But If I dont have my headlights on, and hit the brake, It works just fine. Anyone ever had this problem before? It sounds like a grounding issue to me, but I cant find anything wrong.

[kwmech]

That is a new one on me, different circuits. Try unplugging the turn sig switch and see what happens, may have 2 problems. What about the hi-beams

[VetteVet]

I don't think it's a ground problem cause the light works as long as you don't step on the pedal with the headlights on. KW is right about the different circuits. The wiring diagram shows the taillight on the left side powered by a 18gauge yellow wire. The headlight switch also powers the tailights both in the half out and full out positions. The circuit also runs through the turn signal switch wiring in the column. Have you had that out or installed a new column before this problem?
One thing that comes to mind is when you step on the brake it cancels the brake light if the turn signal is on to that side. Could the wires be switched or the bulb be in so that the tail light is in the brake light position? I know that the lugs on the bulb are off center to prevent this but I've seen it happen. There is a wiring diagram thread in the FAQS on page 2. I have a 1967 to 1987 Haynes manual I will read to see if I can be of more help.