Troubleshooting 4-Pole Running Light Circuit on 2015 Ford F-250 Super Duty

Question:

on the 4 wire connector OEM i have power out to the brakes lights, flashers and turn signals, but not the trailer running lights. the truck lights are fine but with the headlights on, there is no power out of the connector for trailer running lights. do i need change a fuse or relay and if so, which one? this is a new problem as i have been towing both a small trailer and a small camper with this truck for 2 years with no problems.

asked by: Nick

Helpful Expert Reply:

I suspect the issue with the running light circuit on your 4-pole trailer wiring setup is either related to internal damage or corrosion of the connector. Since your truck headlights still work we know that circuit is active. Unless you can find a blown fuse for 'parking lights' or 'running/tail lights' in the power box I would suspect the connector, especially since it is permanently located outside the truck where it is exposed to the elements.

Corrosion can build up inside a connector and often be hard to see from the exterior view. It may also occur at the connection point on the frame rail for a 4-pole like # HM11140755. This item offers an easy-install and low-cost replacement 4-pole.

Does the issue occur with both of your trailers? If so, then that pretty much isolates the problem to the truck.

expert reply by: Adam R