Troubleshooting 7-Way Installation on Ford F-150

Question:

I am experiencing an electrical problem with the trailer wire harness i only have power at the taillight pin but have all lights on truck any suggestions on what could be the problem many thanks

asked by: Garyclair

Expert Reply:

If you are using the Tow Ready Ford Replacement OEM Tow Package Wiring Harness # 118242 and you have a signal at the pin for the taillights (the pin at the 11-o-clock position as you look at the 7-way, see photo please) but not at any of the other pins then there are several potential causes you can check out.

First, make sure the included fuses and relays are fully inserted into the correct receptacles in the truck's power distribution box. Make sure any fuse or relay that is marked trailer/towing is in good condition. It is easy to check to see if a fuse is blown but not so much for relays so trying a brand new relay is the easiest way to find out if the old one is damaged.

Next check that the contacts in the 7-way socket are clean and free of any discoloration - even slight greenish or whitish discoloration can indicate oxidation/corrosion that could cause a problem. Repeat this same check on the trailer connector's contact surfaces. Clean with an electrical contact cleaner as needed.

Next you can check the OEM connector on the truck, where the harness plugs in, to make sure there is no problem with its contact pins (again corrosion is one possibility, along with maybe a bent contact). Trapped dirt or moisture could also cause signal interference.

If you have a circuit tester like # PTW2993 you can test the pins on the truck 7-way (without the trailer connected) to see if the signals are reaching the socket. Have a helper sit in the truck and activate the lighting functions one at a time while you apply the grounded tester to the appropriate pins. Again, please refer to the linked photo of a 7-way to show you which pin to test for each function.

If the signals are not present on the 7-way's contacts, the unplug the harness from the OEM connector and test the pins on it. If signals are present there then you know the 7-way socket is the problem; if not the issue is upstream of the connectors and you might trace the wiring back up forward as far as you can to check for signs of damage like worn insulation or damaged wires.

Once you find and correct the problem you can protect all plug-in connectors with dielectric grease # 11755.