Trailer Running Lights Work with a Chevy Truck But Not with 3 Different Ford Trucks  

Question:

Expert Reply:

Unless someone wired in the trailer connectors on the trucks, and they are not factory or plug and play types of harnesses then they could be wired differently. But otherwise, Ford and Chevy trailer connectors will be the same.

It is possible that there is a ground issue that the Chevy harness does not have a problem with but the Ford wiring does not like. To determine if the issue is on the truck or trailer side you can use a circuit tester like # PTW2993 if you do not already have one and test the truck side trailer connectors on the Fords. Use the wiring diagrams in the FAQ article I have linked to make sure they match the configuration on the affected trucks.

If the running light circuits do not work on all 3 Ford trucks (very unlikely) then it could be a blown or missing fuse or relay. Use the trucks owner's manual to find all of the tow package wiring fuse/relays locations to check them.

If the trucks all check out fine, then the issue must be on the trailer side. Make sure the main trailer connector ground is attached to a clean and corrosion free bare metal surface. Do the same for each of the lights. If the trailer has an aluminum frame, tilt bed, or folding tongue it will help to run jumper grounds from the lights to the main trailer connector ground.

Also check the trailer wiring for any nicks or breaks. And always make sure that the truck and trailer side connectors are clean for a good connection.

expert reply by: Michael H

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