1998 Chevrolet Monte Carlo

I have a 1998 monte carlo that I can not seem to fix brake lights. The rear third light works just fine when appling brakes but the other two just work when they want to. I change the switch on the pedel and all bulbs and fuse but still the same. I am so confused I need help.I tested for power at switch and that is working but when I tested the sockets on the brake lights I get nothing. But when the deside to work I get power everywhere. They only work limited time. They are stubburn! Please help thank you.
October 6, 2007.

Souds like an intermittent short, you will need to trace the wire back to the stop light switch.

Oct 6, 2007.
I have a very similar problem the third brake light works fine. The bottom two don't. I checked the bulbs they seem to look good (the filaments). I know that the trunk was replaced and that the wires were left disconnected. I tried to splice them back together but that didn't fix it. I looked at the fuses all of the transparent ones are good. The plastic gray ones I dont know. Anyways, I wanted to know if there was anything else I could test or what to test or any other suggestions

Oct 23, 2007.
We just fixed the same problem and dont ask why but gm runs the brake lights thru the turn signal we replaced the turn signal switch and no more problems was not easy but the part was 60.00 at auto zone

Jun 14, 2008.