We're getting the "Check Trailer Wiring Message" . We've replaced wiring to the trailer connector, no longer OEM. Also replaced Gamem Controller. Had our neighbor hook up his GMC Sierra and he didn't get the error message. This makes us assume it's an issue with the truck. Anyone have any experience or suggestions? We YouTubed and found some models have a relay switch under the spare tire but 2016 model looks different. Thank you 😊

 

Did you just replace the wiring or did you replace the plug as well? Is the message happening as soon as the trailer is connected or do you have to be in motion?

I’ve only seen a few of these with this issue and all but one came down to a loose/weak connection at the trailer plug. The one that didn’t had brake wiring running through the axle tubes that had barely rubbed through in one spot and so it wouldn’t trigger the message until it was in motion.

Don’t let your neighbors truck fool you into thinking the trailer plug is fine, unless your neighbor pulls your trailer more often than you do.

Wiggle test the plug while it’s connected to the truck - up and down, side to side, and rotational twisting to check it. If the message turns on and off, the truck plug or trailer plug is at fault.

Also verify all the trailer fuses are good. There’s some in the underhood fuse box, but there might also be some in the left side cabin fuse box as well. Check owners manual to be sure.

 

You may get this warning if you have a bad ground. The truck knows when your trailer's wiring is malfunctioning.

Is your trailer wired where every light (or brake if you have electric brakes) has a direct ground wire and not using the trailer frame as a ground?

If the trailer frame is providing the ground, then it may be getting its ground through the hitch ball. So as you drive and the trailer moves around on the hitch ball, the ground loses and reconnects constantly. This may explain why it worked on your friend's truck. Did your friend drive around at all? Or was it just a quick connection in the driveway?

The best way to cure this is to make sure every light has a direct ground wire from the connector (plug) at the front of your trailer. If you want to jury rig it, you can run a wire from the plug's white wire to the metal of the trailer frame, but it's best that everything has a dedicated ground wire. It's OK to run one white wire to the back of the trailer and tee off to each light. It's just not the best installation when the frame is used as a ground.
hope this helps...