The brake lights on my 2003 chevy 2500 hd duramax truck 4-wheel drive does not work. I have brake light on back of cab and trailer brake lights. All fuses are good, brake pedal switch is good and circuit board is good. Need help on finding problem

Do you have diagrams?

Moved from "General GM Chat" to "GMC/Chevrolet Truck/SUV"

First thing I'd do is get a test light or volt meter, pull the taillight housings out, unplug them, and see if power is getting there.