I have a 1986 Trans-Am with the 305TPI.

Here’s the problem- When I turn on the headlight switch, not only do the headlights not come on, but everything that is on that circuit (interior lights, radio, power mirrors, power hatch) goes out. No fuses are blown, and after cycling the ignition a few times the radio, interior lights etc. would start working again, that is until I tried turning the headlights on again. I replaced the headlight switch, which did nothing. I finally found a lose ground on the right rear of the engine. I cleaned all the connections and tightened everything up. The headlights and everything else worked great, for about three weeks, then it started all over again. I rechecked, re-cleaned, and re-tightened the ground, but that didn’t solve the problem. Originally when this problem started it was only an occasional occurrence, but became more and more frequent, and the number of times necessary to cycle the ignition to get the rest of the equipment to start working again, keeps increasing. In fact, the last time I tried the headlight switch was last Friday, and the radio, etc. still haven’t come back online. Any help would be greatly appreciated! This is killin’ me!

 

I wonder if it could have anything to do with the circuit breaker??? It's just an idea. Have you looked at a wiring diagram? You oughta see if all those things ground in the same place. Or it could be a fusible link making a bad connection, but I don't know why that would be affected when you turned on the headlights. But check it out anyway; electricity does weird things sometimes. I don't know about your car, but mine (91 305 TPI) has 6 fusible links total. Three of them are coming off the starter, and I forget where the other three are. I'm pretty sure that the one for the headlights is attached to the starter. Make sure that bolt holding all the wires to the starter is making a good connection.