Hello, I have a 2004 Expeditioin with a tow package with a 4 pin trailer plug. I want to add a 7 pin. I have the wiring for the trailer brake in the back but nothing for trailer battery. There is a spot in the fuse box for a relay (R05) but no relay. Does anyone know if you can add a relay, and if there is any wiring already in place for this. Or would it be better to run a new wire from the battery to the trailer plug? Thanks.

 

I would call your local trailer shop or call a local ford dealer.

 

I would say that you need to try a relay but if you don't have the 7 pin plug on the back there will be no wires there. You will have to run new wire for the 12v and install with the key on only . You could run from the battery but you don't want this because you will drain the battery with the engine off . You will also need to install a fuse protection for this.

 

I would stop by a trailer shop, most all trucks are wired for it but just have a different pig tail from around the spare tire area to the bumper. A good trailer shop or RV shop would be able to tell you real quick. Could be as simple as a new pig tail and relay and you'd be all set. Worst case, you have to run your own wire but I doubt that as then ford would have to have more than one set of chassis wires for a specific vehicle which would get expensive to maintain.

 

I switched out my 4-flat for a 7-way on my 1998 F150 by swapping out the harness and adding the two relays. I doubt that Ford would go back to the old way where you had to run the extra wires yourself.

It should be wired up to the connector located on the left hand side of the frame near where the spare tire is. You're going to need to get a new harness for the back. That will have the new 7-way connector, a ground terminal, and the section that plugs in there by the spare tire. Then you can use the factory gray plug under the dash for your brake controller and everything. Be sure that the ground is attached to a clean part of the frame. Hopefully it will go in the same place it went on the old harness.

In addition to that harness, you'll need to get two relays. You need to get the Trailer Battery Charge relay so you can have a 12 volt on tap to charge a trailer battery or run a light. There's also a trailer backup light relay, which will work the reverse override if you tow a boat trailer or light up backup lights if you're lucky enough to have those. I think you'll already have all the fuses in place that you need.

 

Go to your local parts store or better yet Ford Dealer and tell them what you have. My dealer not only knew what I was asking for, he copied of page from the repair manual, so I could make sure of the relay's location. Nothing to it.