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Troubleshooting Trailer Turn Signals that Work with Headlights Off But not On  


Brake lights do not work on my Kiefer trailer with 2004 Durango lights on or off. Turn signals work with lights off but not with lights on. When lights are on indicator on dash flash fast. Front turn signals work on vehicle but not on back.


Expert Reply:

It sounds like the wiring of your trailer is at fault based on what you described. It sounds like your brake/turn signal functions are run to the running light circuit of your trailer. However, you should first test the wiring of your vehicle to make sure the problem is on the trailer side.

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. What you described can sometimes be due to the converter box shorting out.

expert reply by:
Jameson C

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