[AJT1961]

Notorious burned out plugs/sockets connecting the taillight assemblies to the wiring harness. There are many posts in this thread about the problem and it's pretty easy to fix. If you pull off your rear taillights and unplug them and inspect the plugs and sockets, you'll probably see your problem. If that's the problem, you'll need to replace the offending socket assembly along with that portion of the wiring harness (GM sells a kit for this). It can cause a lot of weird things to happen like the TCS light going on, multiple rear lights going on when you apply your brakes, and your turn signals speeding up when you apply the brakes.