GMC Troubleshooting Questions? Ask a Mechanic for Answers
Hi and thank you for the question. My name is ***** ***** I'll do my best to help. After reading your description, it seems to me it's a clear cut case of a poor ground circuit for the turn signals / IP cluster. Now this ground issue my be in the light bulbs themselves (yep a shorted to ground bulb can cause power back feed without blowing a fuse). Another common ground circuit is trailer wiring, assuming there is trailer wiring on your vehicle. To check the bulbs for the culprit, you'll have to remove all turn bulbs and brake bulbs. Replace each one, one by one to see if the issue changes. Also inspect the trailer harness connection. You're looking for corrosion of any kind. I will look up which grounds to inspect...I'll be right back with you
I'd like you to check ground G400 (LR corner of the interior cabin by the D pillar), G401 (RR corner of the interior cabin by the D pillar), and also check G101 which is in the engine compartment by the thermostat (assuming you have a V8)....check these ground for looseness, corrosion or broken wires...let me know the results.