Brake lights stopped working on my '87 GXL. Stock wiring, as far as I know. Taillight bulbs are fine since the taillights turn on when I turn on the headlights. I did use a testing lamp on the middle brake light and taillights and had someone depress the brake pedal, but there was no light in the test lamp. All of the fuses look OK, but since the fuse box cover for the interior fuse box is missing, I couldn't tell if the correct fuse was being used in each slot. I have since printed a picture of the fuse box and description of the fuses from the FC FAQs. Tomorrow, I will try readjusting the brake pedal light switch. I may also go junkyarding for one if I have time.

Is the fuse slot marked "Stop" the correct fuse to check for the brake lights?

Besides adjusting or replacing the brake pedal light switch and checking the fuses, what else should I be looking for when trying to fix this?

This is annoying since the brake lights are the only reason my car didn't pass inspection.

 

Test the fuse for continuity with a digital multimeter. Sometimes blown fuses still look ok.

 

The circuit works like this:

Power comes in to the brake pedal switch (remember on a 87 GXL there will be two switches on the brake pedal, make sure you are testing the correct one), when the brake pedal is in, the brake switch will send the power to the CPU (4 pin plug on the bottom of the CPU). From there it loops out to the brake lights.

If it was a bad bulb the STOP indicator would light on the dash board. You can not say the bulbs are good by having the tail lights work. Think of the brake light bulb as having to bulbs in it. One for the tail lights and one for the brake lights. That is why the CPU monitors the bulbs and will turn on the STOP light if there is a blown bulb.

So you should test at the correct brake switch and make sure that there is power at the switch, and when you press the switch then the other wire should go hot.

Then check the CPU's 4 pin plug and make sure that the brake wire going into it has that same power when you press the brake switch.

 

Thanks, I didn't know that. I'll go through all the fuses with a multimeter.


OK, I wasn't quite sure how the stop light circuitry worked. There aren't any idiot lights on right now. I'll test the current switch tomorrow. I also got another brake pedal light switch from a scrapped '87 GXL today while junkyarding for parts. If the currently installed switch doesn't work, I'll swap in the new one and see if it helps.

 

I think the brake light relay in the CPU is toast. All of the fuses tested OK, as well as the rest of the wiring, and the junkyard switch didn't make any difference. I'm not surprised, since the circuit board that contains the horn relay and door buzzer were already dead when I bought the car (the horn is jury-rigged to work with what looks like a doorbell).

I've already removed the CPU from the car. Would resoldering the connections work?

 

I think the brake light relay in the CPU is toast. All of the fuses tested OK, as well as the rest of the wiring, and the junkyard switch didn't make any difference. I'm not surprised- I think the circuit board that contains the horn relay and door buzzer was already dead when I bought the car, because the horn is jury-rigged to work with what looks like a doorbell mounted on the instrument cluster surrond.

I've already removed the CPU from the car. Would resoldering the connections work?

 

Sorry about the double-post.

I took apart the CPU box and found quite a few bad soldering connections on both the horn relay board and the brake light relay board. I resoldered them today and it all seems to be working fine now. Thank you for your assistance.