Troubleshooting Trailer Running Lights Not Working on a Trailer Towed by a 1998 Ford F-150


no running lights. turns and brake light are ok. Is there a fuse Im missung somewhere?

Expert Reply:

It is possible that there is a fuse or relay that needs to be inserted on the truck to allow the running lights to function. You will need to consult the owners manual to find the location of the tow package fuses/relays in the power distribution box to see if any are missing or need to be replaced.

The Ford Replacement OEM Tow Package Wiring Harness, # 118242, comes with fuses and relays for reverse lights, battery charge (12 volt power), and electric brakes but not the running lights. I have included a link to the installation details for reference.

What you can do is test for the running lights at the trailer connector on the truck using a circuit tester like # 3808. If there is a signal at the trailer connector then you know the problem is on the trailer, most likely a bad ground at the trailer side connector or at the tail lights. Grounds should be connected to a clean and corrosion free bare metal surface.

If the signal is not present on the vehicle side connector then you know the problem is on the truck side wiring. If a fuse or relay is not the problem, then you will need to trace the wire back until you find the problem spot. I have included a couple of FAQ articles that should help. One covers wiring situations that apply to your truck and the other covers various trailer connectors and there functions.

expert reply by:
Michael H

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