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Adding a 7-Way Trailer Connector to a 2003 Ford Expedition with Factory 4-Way


I have the factory 4 pole connector but need to tow a trailer with a 7 blade plug. Can you tell me what I need to purchase?


Expert Reply:

On your 2003 Ford Expedition follow the 4-Way connector wiring forward on the vehicle until it meets another connector. On this forward connector, if you peel back the loom covering the wires you will see there are more wires going into the plug than coming out to go to the 4-Way, There should be an orange wire and a blue wire.

You will need these wires if you intend to install a 7-Way and the trailer requires 12 volt power and has electric brakes.

You will need 4- to 7-Way adapter # 37185. The 4-Way will plug into the mating 4-Way on the adapter. The white wire will ground to the truck frame. The black wire will connect to that orange wire for 12 volt power, and the blue wire will connect to the truck blue wire for output to the trailer brakes.

The purple wire is for reverse lights and you can tap into a reverse light wire. If the trailer does not have reverse lights then you can just tape up the purple wire and stow it out of the way.

To install a brake controller I recommend the P2 # 90885 and you will also need wiring harness # 3035-P.

If you just want the light functions to work on the trailer then you will not have to connect the blue, black, or purple wires on the 37185 adapter. You will just need to plug in the 4-Way and ground the white wire to the truck frame.

For butt connectors and other accessories you can use the wiring kit # HM51010 and for extra wire you can use # 10-2-1 which is sold by the foot.

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