[curtis73]

Yeah, the brake light switch is working, but the wires the run the third brake light are different than the ones that work the regular brake lights.

The brake lights, turn signals, and hazard lights in that car ALL use the same filament in the bulb. If you pull that bulb out (its most likely an 1157, possibly a 3057) you'll see two filaments. The wimpier looking one is the bright one for those functions. The bigger one is the dim one for taillights.

So, if the third brake light were on the the same wire, it would flash with the hazards and turn signals. Its on a separate wire. Therefore the most logical solution is that the circuit carrying the brake light juice isn't complete.

- test the green and yellow wires for 12v with the brake on. My guess is that you don't have any. Keep tracing that wire all the way back to its source at the fuse panel until you find 12v and you'll find the problem.

- if you DO get 12v, then the problem is grounding. First thing to do is pull the bulbs and make sure the contacts in the socket are squeaky clean. GM does a very nice job nowadays of sealing them, and your 2000 might even have the plug-in 1157 type bulbs. Do they have a black plastic base, or the metal twist in base? Anyway, trace the grounding wire back to its sheetmetal screw. Many times they vibrate a little loose and they corrode like mad

It seems like a daunting task, but the truth is that its an extremely simple circuit. The yellow wire is the left turn, stop, hazard, and the green wire is the right turn, stop, hazard. Its been that way since the early sixties for GM. You get one wire to that circuit, and one wire to ground it. You might have to pull a couple interior pieces off to trace the wiring, but its just a + wire and a - wire that all originates at the fuse block and has a switch at the pedal.