Troubleshooting Left Side Trailer Lights Not Working

Updated 05/24/2018 | Published 05/23/2018

Question:

I own a 2010 gmc sierra. when I plug my 7 way connector in I dont have left brake or turn signal. All of the lights on the trailer are working. Im not getting power on the left side. The left lights on the truck works but nothing on the trailer.

asked by: Thomas B

Expert Reply:

If just the left side of the lights on your trailer are not working, then there is likely an issue with the wiring on that side of the trailer. To be sure that the issue is on the trailer side, and not on your Sierra, I first recommend using a circuit tester like # PTW2993 at the 7-Way on your truck. Test the left turn/stop circuit on the connector (pin at 9 o'clock position) to see if you get power there with that function activated on the truck. If you do get power, then you know the issue is on the trailer. If not, then you will want to make sure there are no damaged or missing fuses on the truck that need to be replaced.

On the trailer, I recommend inspecting its 7-Way connector for any debris or corrosion inside the pins, cleaning as needed. If the connector looks good, then you will just want to run along the wiring on the left side, looking for any damaged, pinched, or exposed wiring that needs to be replaced. Also make sure that the grounds are attached to clean, bare metal surfaces. Then check the light assemblies themsevels on the left side, making sure they are in good condition and grounded securely (whether through their mounting hardware or through a dedicated ground wire, depending on their design).

If you are still unable to resolve the issue, please let me know and I will be happy to look into this further.

expert reply by: Chris R