Testing the Running Light Circuit on a 4 Pole Trailer Connector

Question:

I just got a 2012 Jeep Liberty and transferred the hitch and wiring harness from my 2009 Jeep Liberty. I believe the old harness part number is #118554 but i am not 100 sure. The problem I have now is when I plug the trailer into my Jeep, the running lights come on without the vehicles lights being on or the vehicle running. The brakes and turn signals work. What could be wrong?

asked by: Ron

Expert Reply:

If you are not sure of the exact wiring harness you are using on your 2012 Jeep Liberty, then you could be using a wiring harness that is not compatible with your new jeep. The T-One Vehicle Wiring Harness, part # 118554 is the correct wiring harness for your vehicle.

If you verified that you have the correct wiring harness, then it sounds like the converter box could have a short allowing constant power to run through the running light circuit, or the brown wire on the wiring harness going to the 4-pole connector. I would recommend disconnecting the trailer and using a circuit tester like part # PTW2993 to test if power is constantly being pushed through that circuit. If there is power running through that circuit, then that means the converter box was shorted and the wiring harness will have to be replaced. I have included video links demonstrating how to test the individual circuits and how to test the converter.

expert reply by: John H