Signal light issues on a 2006 GMC Sierra 1500

[Herbert Bell]

Both sides of the signal lights and center cab exterior light flash upon signaling left or right? I already check the fuses and bulbs. (2006 GMC Sierra 1500) I also pulled the flasher and inspected it for any visible issues. In addition to that I swapped the tail light circuit board with a new one to eliminate it as the problem. Unfortunately that's not the issue either. Any suggestions?

 

[Doug_Scott]

You need to follow a logical test plan. Locate and disconnect the wiring harness plug at the rear of the truck. What you are trying to do with this is remove all sockets, bulbs, and wiring from the harness plug rearward. See if the issue still occurs on the front lights. If it stops, you have narrowed it down dramatically.

Repeat this on the front harness. Same reasoning.

If neither of these fixes the issue, then you have to test signal flasher. If your truck has one of those multi-wire flashers, I am pretty sure the flasher itself handles the logic of controlling the signal/brake light separation. Do not know the actual test procedure, but, it must be laid out in the manual that you can likely locate online. Flasher cost is simply too high to just toss one in to see if it works.

 

Most places do not allow returns on electrical parts, simply to stop diagnosis by replacement with the part being returned if it did not fix the issue. I would imagine what likely happened is that too many people returned the bad part claiming the new part was either defective, or by just not saying anything when returning the part. One of those one (or a thousand) bad apple spoiling it for the rest of us.