Brake lights only work with the headlights off

I have a 1980 c10 silverado stepside and the brake lights only work if the headlights are off. If I turn the headlights on the brake lights and the tail lights won't work. Ive checked the fuses and there all fine. If any one has any ideas I would appreciate it. Thanks

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Check all your ground straps it sounds like a bad ground.

stupid question, but have you checked to see if the bulbs are blown? it uses a 3057 i think, a dual filiment bulb.

Hi
I have 3 mid 80's Chevy c30 trucks that all have similar intermittent problems. One has reached the point where almost no lights work and the wipers are iffy. I have checked all the actual bulbs and the light fixtures. checked out / disconnected the trailer hookups. I can make each item work by connecting a hot lead from the battery. I even pulled out the entire dash. I know the ground strap from the engine to the frame is OK. Where do I look for others?

69Tweetybird--each taillight has a ground behind it as well as a ground under the truck on the left side frame rail at the rear close to the bumper or at the underside of the bed at the left rear. Also check the bolts holding the fusebox to the cab uder the dash. looseness here can create a problem like you describe--also check the connection on the steering column for the turn signals, etc.