Troubleshooting Trailer Wiring Harness Thats Only Putting Out 4-Volts on Running Light Circuit

Updated 04/25/2015 | Published 04/24/2015

Question:

Installed the C56336 on my 2014 Dodge Durango Limited. Initially, everything worked just fine had all the lights on the trailer. On the way home the tail lights on the trailer went out. All the other ones turn and brakes work fine. Upon checking the voltage output on the brown pin, it shows a constant value of 4 volts, regardless of the headlights being on or off. I know it should show about 12 with the lights on and some negligible amount with lights off. So clearly, there is a problem somewhere but I am not sure how to go about trying to diagnose it. Any help you can provide would be much appreciated.

asked by: Lucas S

Expert Reply:

As a first step, you'll want to use your multimeter and check the voltage entering the black converter box on the input side to make sure there's 12-volts going in while the running lights are switched on.

If you have the correct voltage entering, but not leaving the converter, then the converter bad and the wiring harness would need to be replaced. The most likely cause of this is a short in the running light circuit on the trailer.

Before installing a new trailer wiring harness, you'll want to carefully examine the running light circuit on the trailer. Begin with the trailer connector, and examine if for corrosion or damage. Make sure the ground connection on the trailer tongue is secure and free of corrosion. Trace the running light circuit (usually a brown wire) back from the connector to the taillights. Look for pinched wires or wire with worn or cracked insulation that would allow the copper conductor to short out on the trailer frame.

I'll link you to some trailer wiring and troubleshooting FAQ articles that you might find helpful.

expert reply by: Mike L