2013 GMC Trailer Light Problem Troubleshooting

Question:

I am connecting the trailer lights to the truck for the first time. Its a 4 flat plug and I have the adapter connected. But its not working, the lights arent lighting up at all. Is there something I have to connect under the hood? Any help would be greatly appreciated.

asked by: James C

Expert Reply:

The first thing I would do is use a circuit tester like our part # 3808 and test the functions of the connector on your 2013 GMC Sierra and then connect the adapter and test the functions again on the adapter to see if the voltage is coming through the adapter. I attached a video on how to test the circuits.

If the voltage checks out there then you know the problem is on the trailer wiring, and if the trailer lighting or wiring is brand new the first place I would check is the grounds for the light assemblies. Make sure the grounds are connected to a clean metal surface. Some light assemblies ground through the mounting hardware, if that is the case you need to make sure the assemblies are connected to a clean metal surface as well.

The next places to check would be the connector for corrosion or the wiring for cut or exposed wires and fix as necessary. You will want to basically inspect the condition of all of the wiring. I attached an FAQ on trailer wiring for you to check out as well.

And if the vehicle connector does not read any voltage you will want to check the fuse boxes for trailer wiring fuses and check to make sure they are good. You would not need to make any connections under your hood either. Thats only for when activating the brake output circuit and 12 volt accessory for 7-way trailer connections. I attached an FAQ on that for you to check out as well if you are interested.

expert reply by: Jameson C