I have a 2010 E-150. I ordered it without the rear step bumper and could not get the trailer tow package with the standard bumper. I have the four pin. I need to go to 7 pin now. The van actually has the dash fuse and also the relays under the hood for brake, 12 volt, etc for the trailer and they are hot but I cannot find any plug under the dash or at the rear o the van.
I was going to just wire the thing until I found the relays and fuse so I would rather use what ford has already put there. Problem is that I can't find where the relays feed in the harness. It seems strange that ford would go to the expense to put all of that in and not use it?
Any help would be appreciated.

 

Somewhat amusing when new vehicle buyers don't ask their dealer such questions. When you've "ordered" a new vehicle, you've paid handsomely for FORD trained dealer product support.

I'm not sure how 2010 E-150 trailer wiring is set up. However, if it's like older FORD trailer wiring, it should've been very EZ to find the all important connector "at the rear o the van". All you'd need to do is follow "the four pin" pigtail back to where it plugs in.

As to "cannot find any plug under the dash" I am sure that wiring changed when the OEM in dash brake controller appeared. If you don't have the Upfitter Switch option at top of dash, there's a blanking plate. I'd expect the plug you'd need to access for trailer brakes would be behind here, NOT really "under the dash" like the older trailer brake umbilical, located next to bottom of steering column

 

as CW kinda mentioned, you follow the harness from the 4-pin connector forward, it runs inside the left frame rail. when you follow it far enough, you'll find a plug where the rear section of harness connects to the front section of harness. the connector with the other functions should be right next to it, and there should be a harness available for it that you can order from your dealer, or maybe elsewhere

 

Actually it was not that I did not ask or know that there was no 7 pin wiring. They would not sell me a truck with a chrome bumper and tow package, only with the ugly step bumper could I get the tow.
The thing is that, when I went to wire for 7 pin, I found the relays in place and hot. Odd that ford would put the relays in and wire them but have no wire run from them so I figure there must be wiring somewhere! It's a shame for me to wire right past relays that are already there.
I have fords here from 1955 to 2011 BUT after this van there will be no more ford vans! 55 still running, F-150 great, MKS eco fantastic....
Our business has one GMC and one chevy. They drive better and ride MUCH better. Ford's "packages" just don't cut it. Since I drive this van (cargo van) all the time, I wanted heated mirrors, etc. I could get them on a pass van or upfitter but not on a cargo van! It's like the tow package. I dosent make sense. I did get sync though. It did not work from day one and still does not. Ford just sort of hold their hands up with no explination. I paid several hundred dollars for nothing! As you can tell it pi$$es me every time I get in and look at the dash plate "Microsoft".
Sorry for the rant and thanks for the reply. I'll dig farther up into the dash.

 

Thanks, I did find wires that came out of the same group as the 4 pin. It was 7 wires that went to a plug that plugged in to another blank plug that bolted to the left frame. None of these wires were hot and not the correct colors. I tried to trace up the left side but I did not find anything.
I went to the dealer and they could only sell me the & pin hitch plug for a bit over 100 bucks. Apparently, ford offers no overly harness or other way to convert to 7 pin. Wow!
The next thing to try is hooking a tone generater to the relay plug and see if I can find anything down stream.

 

what a mess! i know for sure that the wiring i described is accurate and functional on vans several years older, and was under the impression it held true on newer vans too. apparently it doesn't.

you might try to see if you know anybody with a similar van and a tow package and see if they have any wiring you could learn from... or try as you mentioned above to better track things.
i agree with not wanting to bypass the relay group made for the purpose, but if it'll be that much of a PITA, it might be your best bet

 

Good idea! Now you have got me looking for vans with a 7 pin out the back!

 

I had this exact issue with my 2008 E350. Without a tow package, there are only wire for a flat-4 connector ran to the back of the van. The other wires, brake, 12v constant and reverse terminate at a large connector block on the frame, under the area of the drivers feet. The outside (heavier guage) wires are the ones that you need. (wire colors makes sense at this point) I cut them from the connector and spliced wires from there to the back of the van. One of the relays (I think for the constant 12v) was not in installed and had to be purchased locally.
There is a connector for the brake controller ready to go under the dash.

Jack