Recommended Parts for Re-Wiring 5-Pole Flat Boat Trailer to Match Truck 7-Way Wiring

Question:

I have a boat trailer with a flat five pin connector that worked fine when attached to a flat five pin connector on my former truck. I recently bought a new truck a 2012 Ford F1 50 with the round seven pin connector. I bought a seven pin to five pin adapter but only get running lights no brake lights or turn signals. The truck fuses look to be intact from what I can see. I replaced the fuse for the trailer signals and brake lights to no avail. Is it possible to seven pin connector is set up somehow differently by the former owner or is there another fuse or relay somewhere that I missing. The trailer lights are nearly new and worked perfectly on the old truck. Thoughts?

asked by: Bill B

Expert Reply:

Adapters like # 37385 and # HM47570 are convenient and can work fine for the short-term but for long-term reliability you are really better off replacing the connector on the trailer to a 7-way that matches your truck with no adapters - or their potential problems. Those extra connections can mean more chances for corrosion.

You can easily test your truck's 7-way using a circuit tester like # PTW2993. Have a helper activate each function while you apply the tester to the appropriate pins on the 7-way. Please refer to the linked article for help identifying the function on each pin. You can also test the trailer by applying 12V power direct to each of its pins while it is not connected to the truck. If both truck and trailer test okay when the adapter is not in use, then you've got your answer: either the adapter is bad, or it is wired differently than your truck and trailer.

You can use a 7-way plug like 8-foot # H20046 or 6-foot # H20044 and join that to your trailer wiring using junction box # 38656. You'll need ring terminals # DW05702-1 (10) and # 44-5310A (2) to complete the installation. Match wiring by function, not by wire colors. Again, refer to the linked article.

Dielectric grease like # 11755 will help to protect those new connections.