Have you checked the fuse?

Honestly I cant find the fuse for the lights. I found two fuse boxes and none are for the lights.

now i have had 2 of these trucks no... im no mechanic but just a driver.. i would first check the brake light switch... i think it is called thta... it is in behind your brake pedal.. it is only a 20 dollar part so not too expensive.. it looks like a tan covered box... it is a simple desing i only know it is behind there (if your electric brake pump not working with the ignition off that will most likely be the problem) If that does not do it check your fuse box and make sure when the truck is running you hear a clicking comming from it when you push on the brakes... if you dont it may be an electrical problem ( our truck had a hands free and radiio put in aftermaket and the attached the wires to thwe brake wiring and it slowly pulled out the wiring out of the fuse box) dont know really how your truck is rigged up. If i remember correctly the are quite a bit of fuses for the brake lights... 1 one each side for the truck and the trailer. Check to see if you have power in the fuse box under the hood... if you have power there and no power in the cab fuse box there is a problem in the wiring between under the hood and your fuse box.. it took our mechanic 2 days to find it but i have had this problem with both of them that i have driven and they have both only had 90000 kms when it happened.

There is definately a fuse for the brakes, it most likely is bad. The fuse is to protect the switch and wiring. Did you try disconnecting the trailer harness and reconnecting the original plug? It might be a broken wire or corroded pin on one of the plugs.