Diagnosing Non-Function Running Lights on a 2007 Ranger Boat Trailer Behind a 2007 Ford F-150  

Question:

Expert Reply:

If you have already checked the 5-Way on the truck and it is working properly, then you have narrowed the problem down to the trailer.

Typically grounds are the source of most trailer light problems, but since you have the other functions, ground issues are less likely.

Check the connector on the trailer for corrosion. If they are dirty or corroded, clean the contacts with a wire brush and some electrical contact cleaner. Re-apply dielectric grease like part # 11755 to keep moisture out and keep the connection clean.

Trace the running light wire, again typically brown, along the trailer. Check for nicks, frays and loose connections. Just the slightest bit of contact between the copper and the trailer frame can cause the circuit to short to ground and the running lights would not work.

Finally, inspect the tail light housings. It never hurts to check your grounds, so go ahead and do that. The running light bulbs can burn out, so check that as well. If you have additional sidemarkers, they can also be the problem. Check those grounds as they could be breaking the circuit and not causing the other functions to fail on the main tail lights.

expert reply by: Patrick B

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