Brake lights wont work right tail light wont work 2003 gmc envoy

ST/LP, Fuse 12, 25 Amp - feeds battery positive to brake switch ORN (orange) and out the WHT (white).

Test with a simple automotive incandescent test lamp to ground. Test lamp should light on both sides of the fuse and with contact to the switch ORN and to WHT while brake depressed.

The tail light fuse is under the rear seat on the drivers side.

Start with changing bulb

trace all your wires theres a break somewhere

Since the high mounted brake light works you know that the brake light switch is working. Now you need to check the brake light bulbs in the rear tail light assemblies. The brake lights are separate from the tail light (parking or running lights). There are two screws that hold the rear light assemblies in place.

First and easiest we need to check for power going to the rear lights at the plug that goes into the tail light housing. There is a board that the lights plug into that goes bad. The Envoy uses separate brake and turn bulbs so the 3rd brake and the two side are on the same circuit.

Which of the tail lights comes on? Is it the parking light or brake light? And is it only one side that is coming on? This is a very strange symptom. The Body Control Module (BCM) controls the light and could be the problem, but before replacing it, a good diagnosis needs to be done.

brake light switch or bad groung at the lights

theres usually a pressure switch behind the brake pedal, sometimes the plastic hex nut rattles loose and you have to retighten it.

sounds like a fuse look under the dash panel for fuse cover look at the back of cover and check that fuseThanks for using fix ya Please rate my response thank you very much