Troubleshooting Trailer Wiring Where Running Lights and Blinker Dont Work

Updated 10/22/2018 | Published 10/21/2018

Products Featured in This Question

Curt T-Connector Vehicle Wiring Harness with 4-Pole Flat Trailer Connector

(22)

$62.19

Hook Probe Circuit Tester

(61)

$13.33

Question:

The kit worked last year when I installed it. Now I dont have running lights and the Driver side on the trailer is really dim for all of the other lights. The lights on the car are even and bright on both sides. I dont see any broken wires or cut wires. I just replaced the trailer connector coming from the car. The old one had contacted the road and was warn on the open connector from touching the road.

asked by: John G

Expert Reply:

It's very possible the trailer connector dragging on the road could have caused a short once you fixed the wiring. It really depends though on if the wiring was damaged as well and if the connector was attempted to be plugged in.

First thing you should do at this point is test the 4-way of the wiring harness with a circuit tester part # PTW2993 for voltage on all of the right pins when the taillight signals are being applied. Just like in the video I attached.

If the voltage checks out there but the trailer lights still don't function right then the problem is on the trailer wiring. That would mean that problem is either due to a ground issue or a short issue.

Make sure that the trailer side connector are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and corrosion free bare metal surfaces. If there is anything between a light ground and the metal trailer frame or if the trailer has an aluminum frame, tilt bed, or folding tongue, any of these things can interrupt the ground. Running jumper wires from the light grounds to the main trailer connector ground can help.

If the problem is on the vehicle side then I would first recommend you double check how the harness is installed on your vehicle, make sure all of the connections are good and tight. You should check all towing related fuses and relays as well.

expert reply by: Jameson C