I have no brake or tail lights on my 71 cutlass convertible. I replaced the ignition switch the turn signal switch and the brake light switch. I am no mechanic or electrician, but i believe something is loose and not touching constantly. Some times when I hit the brake pedal, the park lights in the front bumper and the brake will come on. But only both will work when I'M on the brake not just the brake lights, but I never have tail lights.

 

Nine out of 10 electrical problems are caused by a bad ground, especially when lights go on at the wrong time, like when you step on the brake pedal and the parking lights go on. That means the brake lights are grounding through the parking light circuit instead of directly to the ground they're supposed to. Make sure all the taillight, brake light, turn signal light, parking light, license plate light, etc. sockets are clean and not-corroded.

I had a situation once where turning on the headlights caused the right turn signal indicator light on the dash to light up and stay lit. The turn signal itself did not light, and it did work properly when I signaled a right turn. But the right side dash turn signal light stayed on whenever the headlights were on. The problem turned out to be the turn signal light socket was corroded and not grounding, so the parking light at that socket was grounding back through the turn signal indicator light circuit. Weird, but replacing the turn signal light socket on the front right side fixed the problem.

 

Did the lights work before you did all your changes? Somewhat related, have you blown the brake light fuse? I just went through this exercise with a turn signal switch on a 66 Chevelle, the turn signal metal stalk was shorting the brake light circuit when tightened. I wrapped the end where it screwed into the switch with electrical tape.

 

You need someone who IS some kind of electrician to take a look.
I doubt anything serious is amiss, most likely bad grounds like Jaunty said, however a 45 year old car might well have wiring showing its age.

Roger.

 

Did you replace these switches because the lights didn't work previously, or did this problem start with the switch replacement? This is kind of important if you want us to provide you useful troubleshooting information.

 

I recently had wiring issues during a restoration

Someone forced a single contact bulb into the 2-contact tail/stop socket, thus connecting stop and tail circuits.

then, installing the front signals, one refused to work. Bulb tested OK. Removed lamp asm for bench tests, find that voltage gets to the bulb holder but not thru to the housing. They appeared to be crimped together but corrosion and a half-rectal restoration of the lamp left no electrical connection, easily spotted with the volt/ohm meter. Solution was to use an ice pick to enhance the crimp between bulb holder and housing in half a dozen places about the OD.

Use the voltmeter and jumper wires to find out whose path is not working right.