no joke inop brake light head-scratcher
 

I have an 01 trans am that sat outside a many years and leaked inside and moldy that I decided to undertake restoring myself once I realized how well the engine still runs. I'm currently on the electrical chapter of this project haha, and the last major electrical malfunction I'm troubleshooting is the brake lights not working. Do not worry. I read up on as many malfunctioning brake light threads as I could already and even generic internet articles about it. I know that many people have had this problem before haha-- I'll explain everything I know so far, and maybe somebody here would be sharp enough and kind enough to help me solve this. I hate to admit it since it sounds so simple, but it has me scratching my head. First off I bought a power probe to help me solve all the electrical issues. It was extremely helpful and saved me bookoos of time. My brake pedal switch connector reads full positive on one side (all fuses good--checked them at least 100 times at this point now after solving all the other problems) and 0.0 volts on the other side. The probe does not identify it as a ground, just 0.0 is what it says. I traced the wire to a large bundle that exits through the firewall to under the hood. It is lost from that point to me but I suppose goes to the PCM. I even tried bypassing the switch by running a wire from one side of the connector to the other just to make sure. I am aware that the brake light uses the same filament as the turn signals, so there must be a cancel function for the brake light when turn signal is activated. Somebody wrote in one thread that the issue would be the turn signal switch if the third brake light on top works while the two lower do not. My third does not work. It reads ground on each side if the connector. My turn signals and all other lights work perfectly. It isn't the bulbs. I have looked as much as I could for any severed wires and couldn't see any. That hasn't been my issue yet anyways. The issue has been rust and corrosion. If someone has any ideas to point me in a good direction please assist, and thank you much in advance!!! I cannot wait to get this problem solved

have you tried the turn signal switch ? it controls the brake lights

if the 3rd light does not come on ....its the brake light switch.....if 3rd light come on but not main tail lights....try the TS switch....its in the steering column

In this case the turn signal switch would not be the source of the problem because the third brake light also doesn't work and it doesn't route through the T/S switch like the other brake lights.

The Power Probe is one of the most impressive tools available for electrical testing but you have to be careful about interpreting the results. Showing 12V+ on one side of the switch connector and 0V on the other side is perfectly normal if the connector is unplugged from the switch. One side is feed voltage and the other is output to the lamps but without the switch connecting the two, the output side will show nothing.

First thing to check is whether the wiring from the brake light switch to the taillights is good. It's very likely that it is since your turn signals work but it's always good to double check. Use your Power probe to provide power to the light blue wire at the brake switch. This should make all three brake light illuminate. If they fail to illuminate then you have a break in the light blue wire someplace between the brake switch and where it splices into the rest of the brake light circuit (about 3" from where the left instrument panel ground wire splits from the harness). If some lights work but not all then there is a break in the light blue wire between the splice and the light that doesn't work.

There are actually three power supply leads to the brake switch which serve different functions. The two pink wires are for transmission interlock and cruise control. The orange wire is the power supply for the brake lights. It connects to the light blue wire when the brake pedal is depressed. If you confirm that there is constant (battery) power on the orange wire and the previous test with the light blue wire made the brake lights illuminate then you can be sure that the brake switch is the source of the problem.

If you don't have constant power on the orange wire then you need to double check the STOP/HAZARD fuse (test it with the Power Probe or just replace it with a known good fuse). If the fuse is good, look for a break in the orange wire between the fuse panel and the brake switch.

Thank you so much for that information! I believe I wasn’t checking out the brake light switch properly. I’m going to check it today based on what you said. It does sound like that is the problem. I’ll post the results once I check it. Thank you again for explaining that.

Ok white bird oo my head scratching is over. Your information was 100%. What happened was on mine, not sure if they are all this way, there are two switches that get released when the brake pedal is pushed. The one i was checking was fine. I didn't even realize the other one was a switch at first because the pin was seized and nothing moving when i pushed the pedal. In a hurry i figured those wires were just mounted there for convenience. Once you said the switch has more than two wires i realize that was it. I Unplugged it and sent power to the lights and they all lit up right away. So i took apart and cleaned up and lubed the switch, and lights work fine now. Thank you for ending my head scratching! I really appreciate you writing that.

You're very welcome. Glad you got it working.