On my 75 when I turn the headlights or parking lights my right brake light and signal light don't work and the right turnsignal indiciator on the dash is on. As soon as I turn the lights off the right signal and brake light work

Ed

Ed, if your inside indicator is illumoinated, I suspect you have a ground problem. I would check the right side turn and brake light sockets. make sure you have a good ground there. the reason that the inside indicator is on, because the circuit is travelling "back up the wires" looking for a ground and it is finding it in the light socket in the dash.
Good luck

Ed,
I agree with 82dukman, but sometimes the wrong light bulb gets put in. Be sure to check that you have the dual filiment light bulb. I going on memory here... and I'm not a spring chicken anymore... but I believe the brake light should be an 1157 .. good luck

BudD