98 gmc brake lights are acting backwards.

[z71nation]

Hi everyone. I've been working on my 98 and have most all the issues sorted except the brake lights. The third light works as it should. But when the key is off the brake lights are off. Hit the pedal and hey come on. Normal right? Well when you turn the key on, the brake lights come on. Hit the pedal and they go off. When the key is on they are completely backwards. I tried a good used multi function switch. I tried a head light switch. Two brake light switches. Checked all the grounds and even made a few more chassis grounds. Checked the circuit boards in the wires. Checked all fuses and relays. Checked every wire I could open a wire loom on. Is this a bcm issue or maybe an ignition switch? Idk.im about ready to scrap it

 

[eyesi]

rear turn and stop lights use the same circuit , most time you can find the problem at rear end lights wiring, did you checked ground wire there?

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[z71nation]

Yes. I actually in plugged the rear light harness in the engine bay under the brake booster and checked for power there and there was. The brake lights are recieving power when they shouldn't and they don't have power when they should.

 

[joep88cheyenne]

Almost sounds like you may have a cruise control switch installed instead of a brakelight switch. The cruise is on when key is on and opens when brake is depressed and turns off the cruise control. Brake light switch is open until depressed then is closed to turn them on. Third light runs as normal, lights both key on and off?.