Brake light on cab

The third brake light on my 2000 Silverado dosn't work. The bulbs are good. There is no power to the bulbs. I traced the wiring to its entry point at the dash and have no power that far. Could it most likely be the switch? Does the ECU control the light. The truck looks like it had a cap on it before I bought it. Could the light have been disabled through the ECU?

I Have A 96' This May Seem Dumb But Did You Check The Fuse?

I Have A 96' This May Seem Dumb But Did You Check The Fuse?

Yes the fuse is good. I even checked it with a meter.

I am trying to install a "third brake light" which is part of the shell on the back of my "98 Chevy S-10 and can't find the correct wire--anyone have help?