Rear brake light problem

Have you tested the turn signal relay?

This is a common GM specific problem. Your turn signal switch contains an elaborate networking device that has to cancel brakelights while running a turn light. Often times the ground within the turn signal switch is lost causing your situation. After investigating such other possibilities as fuses and loose grounds it may become necessary to replace the turn signal switch. Thank you, Dana

Wrong replacement bulbs.

check blubs if the center light works should be working side brake lights

Sounds like either both bulbs need replaced or a wiring problem. Check bulbs first if they are fine use a test light to see if there is current to the bulb if no current trace back to see where current stops and repair. Also if you have current check your groundsfor the brake lights.

you give some good clues. because your third brake light works but not the other two, and because you sometimes get brake lights if you have turn signals on at the same time, i would say that some wires got crossed up with your other taillights. check out the power wires back in the taillight assembly and the wires that run back to the taillights. something is mixed up back there, now you just have to find it. if all else fails after you isolate which wires are the brake light wires get some new wire, same gauge and roughly same length, remove a bit of insulation but don't cut the wire in two, and put the new wire in as an overlay. if having the new piece of wire there makes the brake light work you found the break in the wire. you can cut out the bad piece and fasten the new piece in. you can solder it if you have the equipment to do that, or you can buy some squeeze in place connectors at the car parts store. either way, good idea to tape it up when you are done. hope that helps

check the multi function switch. I hava a 96 chevy monte carlo and I had the same problem . I changed the multi function switch and the brakes lights now work. the rear brake lights run thru the switch on the turn signal circuit. try it and see.

Have you checked to see if the ground wire from the brake light harness in the trunk came off, broke or loosened up? The third brake light has it's own ground wire. That's why it still works. Have you checked the fuse? Just throwing some suggestions out there. Best wishes to ya.

This is usually caused by a defective multifunction switch, see it quite allot, the clue is the 3rd brake light, it is on a separate fuse and does not run through the multifunction switch on the steering column.