Trailer Running Lights Do Not Work when Connected to Ford F-150

Updated 07/16/2020 | Published 05/24/2015

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Question:

checked fuses seem ok, stop and turn work on trailer but it has no ruinnung lights that work, if dis connect from truck and use a batt, all trailer lights will work, got any ideas, ???

asked by: Tom S

Helpful Expert Reply:

Your Ford F-150 might have relays related to the tow package wiring and not just fuses. Use the owners manual to find the locations of any relays (or fuses) related to the tow package wiring. The easiest way to see if a relay is bad is to use a known good one in place of a potential bad one.

If all fuses and relays are good then the problem is somewhere between the trailer connector at the back of the truck and where it terminates at the front.

You can use a circuit tester such as # PTW2993 to test the truck side trailer connector. If there is no power on the running light pin, then check the back of the connector where the wires attach. Check for any loose connections or corrosion and fix/clean as needed. You can also check the wiring from the back of the connector forward by testing the wire(s) at different spots front to back. If there is a break this is how you would find it.

expert reply by: Michael H

Jason H.

7/12/2020

I have no trailer park lights either. Cannot source the problem so I am direct wiring that pin to my tail lamp.

Chris R.

7/16/2020

If you haven't already I would definitely make sure you don't have a blown fuse under the hood. This seems to be the most common cause for this type of issue. The fuse location(s) related to the trailer running lights circuit should be listed in your truck's owner's manual.