Its probably broken so you you should go to a mechanic but I'm not a professional so i could be wrong
There are a few reasons that the third brake light is the only one working. One reason could be that there is a short in the wires of your main brake light. Another reason is that the light bulb has blown out.
the third brake light is direct from brake light switch no fuse
Begin by removing the wiring harness from your third brake light. Remove the third brake light retaining screws. Reverse the process to install your new third brake light.
It probably indicates that both your other brake lights are burned out and need replacing. BTW: It is illegal in most (if not all) jurisdictions to drive this way.
The brake light, a red light shaped like a headlight on the dash means that one or more exterior lights are not working. It could be a taillight, brake light, side marker, license plate light, or third brake light. It stays on all the time if it's a side marker or any light besides the brake light. If it's the brake or third brake light it will come on only when you press the brake pedal.
blubs blown? Check the turn signal switch.
I would guess that both of your brake light bulbs are burned out, and only the high mount bulbs are still working.
Fuse for the "Third" Brake LightAlthough I have no experience with the Chevy Tahoe, the systems are similar for almost all vehicles.The third brake light is tied into the wiring for the other brake lights and is protected by the SAME fuse they are.Thus, there is no separate fuse for the third brake light.Therefore, IF your other brake lights are working, then a failure of the third brake light to activate IS NOT caused by a fuse, but instead an "open circuit" condition in the "dedicated" third brakelight wiring [from where its wire "splits" off of the wiring harness to the other brake lights].This is usually caused by a connector which has become disconnected, or a cut or broken wire.
how to change third or center brake light on Chevy beretta 95
How to change third brake light in 2009 Hyundai sonata
some cars abs light comes on if your third brake light is not working. check and see if a wire is broken, ect.
How do you replace the third rear brake light in a 2005 buick allure