I'm just saying that if it's only your 3rd brake light that isn't working, see if your cruise control works, if not look for the fuse that controls that (better yet look through all the fuses, sometimes GM piggy backs other things on another circuit fuse), I think it is because the cruise control is tapped into the 3rd brake light (at least mine is) so that when you press the brake pedal it cancels the cruise control speed when you are driving. Hope that makes sense, I saw a chevy tech spend 45 minutes testing everything under the sun to diagnose my dead 3rd brake light then he thought about the cruise control!! Keep us in the loop and good luck!