did you check the fuses?
also check where the wires to the lights plug in under the box at the back of the frame.
there are seperate fuses for the tail and brake lights on the truck.either under the hood or in the side of the dash by the drivers door.
2006 gmc 3500 xcab lb, with the LBZ.
with air dog lift pump, race valve, egr delete, and efi reprogram, thanks to husker diesel.
84 gal fuel cap.34 main and a 50 gal aux transflo system.
20k curt 5th wheel, 20k goose neck.
still stock. 4x4. 430,000 miles and counting.
transporting new units from factory to ia. dealers and ship.
engine replaced at 404,000 mi with one with 118,000 miles.