Troubleshooting Trailer and Vehicle Lights that Turn On with Trailer Connected

Question:

2017 GMC 2500 Denali. The truck can be off with lights off. As soon as I plug trailer in, lights on truck and trailer turn on.

asked by: Kevin V

Helpful Expert Reply:

It sounds like there may be a short somewhere along the wiring on the trailer you are towing.

I recommend first checking both the trailer and vehicle side connectors for any dirt or corrosion, simply cleaning out as needed. If everything looks okay, move to the trailer side and check along the wiring for any obvious signs of short such as cut or exposed wires and corrosion.

Lastly, check to make sure all the ground connections on the trailer are made to clean, bare metal surfaces. Bad or weak grounds can cause a variety of strange issues like this one.

If you are unable to find and resolve the issue, please let me know and I will be happy to look into this further. I have also attached a wiring troubleshooting article that you might find helpful.

expert reply by: Chris R