Troubleshooting Harness That Works Only on LED Light Trailer but Not with Incandescent Light Trailer

Question:

i have this installed on my 2019 terrain hook up to trailor and the left turn and brake lite does not work but the right turn and brake work fine the tail lights and marker lights work fine the trailor has the old style lights bulbs not led lights. Now when you hook up a trailor with led lights on it everything works fine does that mean i have to use the 119250KIT wiring harness

asked by: Ralph L

Expert Reply:

Ralph,

It sounds like the Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector # C94FR is what you should be using for your 2019 GMC Terrain as it's designed for vehicles with a factory tow package. The # 119250KIT, you mentioned, is designed for vehicles that do not have a factory tow package.

LED lights draw only a fraction of the amperage when compared to incandescent lights, so what is very likely happening here is that you're dealing with a case of an insufficient or poor ground. A poor ground may be enough to power a trailer with LED lights, but it won't be enough to power all lights on a trailer with incandescent lights, which explains your situation.

To make sure your harness is properly grounded, find a place on your Terrain where two pieces of metal are stacked one on top of another, as sometimes one layer of metal may be too thin and unable to carry through the necessary voltage. Also, sanding down the area will help ensure the metal is uncoated and the connection has proper contact.

I've attached a video for you showing this process at the bottom of the page.