First Step In Troubleshooting No Trailer Lights When lugged Into 2021 GMC Sierra

Question:

i have a 2021 gmc sierra and i went to plug in light for a boat trailer but they did not work. They guy i bought the boat from move his pick up over and the lights worked. what would cause this problem.

asked by: Louis E

Expert Reply:

Try testing the pins on your connector with something like the Pollak # PK12741 circuit tester to see if your 2021 GMC Sierra is actually sending power back to your trailer connector. Since the trailer worked with the other guy's truck I'm guessing that you might have some fuses or relays to change out (see your owner's manual for the correct locations) but the first step is to see if power is actually being sent from your truck.

After that it's just a process of elimination; determine where you're loosing power and look at the wiring, connections, and grounds on that circuit to make sure they are all in good-working order.

expert reply by: Jon G