2007 Chevrolet Silverado Classic Brake Light Issue.?

I own a 2007 Silverado Classic, when I depress the brakes the Cab 3rd Light comes on but the actual left and right tail light brake bulbs don't come on. I have replaced them and nothing happened. I thought it may have been the switch on the pedal but that would not explain the 3rd light coming on. Any ideas other than bulbs, switch or fuses of what I should do to fix it? Any help would be great. (Also word of advice if you ever get a chance to buy one of these trucks, politely decline as they are utter garbage!)