GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hello and welcome to just answer, my name is ***** ***** master tech here to help I cannot see or hear your vehicle so I rely on your input so I can help you better. I read your input and have a question before we start. Are these factory tail lights and not been modified? does it have a trailer towing light package?
thanx for that info, the problem is in the rear of your vehicle , did you make sure the bulb is a double filament usually no. 1157? also no corrosion on the connectors? after cheching that and all is good I would disconnect the trailer towing modual and see if tha corects it as they sometimes short out internally.