Hello I have a 99 Sierra 4x4 that I just bought and just realized the brake lights do not work. So far I have checked/replaced fuses, bulbs, brake switch, circuit board, etc. I am at a loss as to what the cause could be. 3rd brake light does not work either. The turn signals, park lights, and backup lights work just fine. I tried to check grounds off the tail lights and all the wiring seems to be going back to the circuit board so I don't know where else to look. Any help or places to start looking will be greatly appreciated. Thank you.