Troubleshooting A Non-Working Trailer Connector On A 2020 GMC Sierra 1500

Question:

I have done a ton of research, watched a lot of videos and tried just about everything manual included. My 2020 GMC SIERRA SLT 1500 trailer light connector is not working and I have never hooked up a trailer until trying desperately for 3 weeks now. I have tested all the wiring on the trailer unit itself and everything works great, so the trailer wiring is not the problem. I even checked fuse #82 but it’s not blown. All truck running lights, headlights, etc are working perfectly. I saw a video of a man with the exact same problem but after many many additional expenses and service visits nothing has solved his/my problem. Is there a switch or something that needs to be ON from inside the truck to turn them on when plugged in? I NEVER had even the closest problem w/my 2010 RAM LARAMIE LONGHORN. On the other hand I’ve had nothing but failure after failure with trailer hook/truck connection in the back. WHAT IS THE PROBLEM,? Don’t tell me to take it in to service bc they will suggest and try everything I already have. I’m very very upset and frustrated. What is the permanent fix, please?

asked by: Linda S

Expert Reply:

When it comes to troubleshooting wiring issues you need to start at the power source and work your way back to the light to find where the issue is and fix it. You'll want to start with the trailer connector on your 2020 GMC Sierra 1500. Get a tester # PTW2993 and test each terminal for function (running lights, let turn, right turn, stop). If the tester isn't lighting up then we know there's either a loose connection behind the connector, damage to the wire somewhere between the connector and fuse, or the fuse is blown.

GM released a tech bulletin that basically said they know this is an issue but that they aren't going to cover it under the warranty. They also stated that the ground connection locations they chose can become corroded so I would follow the ground wire back from the connector to wherever they placed it to see if you have a decent ground. I've attached a diagram below of the fuses associated with each function so that you can test each one as well to ensure power is being sent to the trailer connector.

If each function works correctly on the truck's trailer connector then we know it's the wiring on your trailer that's causing the disconnect and you'll need to check all the wiring again to find where the power is being lost.

expert reply by: Kevin C

2020 GM Trailer Fuses
(click to enlarge)

J.r.

11/27/2024

if fuses are good then were should a person look next

Kevin C.

11/27/2024

@Jr Are you getting each signal at the 7-way of your vehicle? If not and your fuses are good then there's a short somewhere in your wiring and you'll have to trace it to find and fix the issue. If the signals are coming through to the 7-way but not for the trailer lights then you'll continue to trace the wiring from the trailer's 7-way cable all the way back to the lights to find the short.

Dale B.

1/18/2025

The Check Trailer wiring and check trailer brake connections keeps going off in my 2020 GMC Sierra SLT when towing our trailer. However when our friend uses the same trailer using his truck, he doesn't have any issues with notifications. This makes us think the problem isn't the trailer. Do you have any ideas where we need to start looking for the problem?

Kevin C.

1/20/2025

@DaleB The sensor in your Sierra is looking for trailer and not seeing it. This is typically triggered by sending out a pulse to the running light circuit on the trailer. If the trailer has LED tail lights there's not enough of a draw for it to see the trailer and will keep erroring out. If your trailer has LED tail lights you can just splice a load resistor # DI34ZR right before the tail lights for there to be enough draw to sense the trailer.