No Trailer Lights When Towing with 2003 Ford F-350

Updated 10/01/2018 | Published 09/30/2018

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Question:

Everything on the truck works as it should, but the trailer lights do not come on. I have checked the connections at the seven pin connector and also at the box connector on the harness. I had running lights earlier but after I cleaned the contacts I don't have anything now.

asked by: Mike

Expert Reply:

I cannot say for certain but based on what you described there are either blown fuses or issues with the trailer connectors. I would first start off checking the fuses. I looked in the owner's manual for your 2003 Ford F-350 and found the following fuses/relays that relate to the trailer lights on your F-350; 6, 38, 39, 101, 115, and 305. These fuses/relays are in the fuse box under the hood.

If the fuses/relays are all good then you need to turn your attention to the trailer connectors. Use a circuit tester and test the wires leading into the trailer connector and the pins leading out of the trailer connector. If you have power going in but not coming out then check the connection of each wire at the rear and then the pins themselves. If the pins are bent or corroded then the trailer connector should be replaced. I recommend doing this for both the trailer and vehicle side.

If either of the trailer connectors need replaced then you can use part # HM48470 for the vehicle side and part # HM48510 for the trailer side. If power is not reaching the trailer connector pins then you need to trace each wire back while checking for breaks or frays.

expert reply by: Conner L