Ok so here is my experience. Bought a 2017 Expedition EL XLT that had a Class IV hitch but no 7 PIN and no trans cooler or HD radiator. I needed to pull my Jeep up to the mountains so when I took delivery I had all of the parts I needed to do the install. Here's what I did.
Parts:
This shows the cubby removed with the factory harness hooked to the back.
You don't need to take off the dash, but you do need to get the panel below the steering wheel removed and the black bottom off the steering wheel unless you have small arms. Here is a shot of what it looks like from underneath. They are the yellow wires on the far right.
The four flat had capped blue wire that even had a tag on it that said "Elec Brake"
I had to grind down the weld to fit the new bracket in place for the 7 way.
I ran a black wire from the fuse box in the front of the Expedition to the rear by following the frame rail and using zip ties when needed. See the black wire connected here. You might want to add tape or heat shrink tubing but I didn't' have time and live in AZ.
I will post a few photos of the finished product and the line from the fuse box since I forgot to take them. Took me about 2 hours to do the work. The last step is to install FORScan, get the extended license (you can get a trial for 2 months for free) and then hook it up to your OBDII. You will need to go to the "Computer" icon and the IPC (As Built) in order to change the 2 numbers referenced in the spreadsheet. FORScan is pretty easy to use but it has a learning curve, you'll get used to it quick but be careful. You must use Windows, it does not work for Mac OS.
My dealer said it would cost me $50 to do the same thing through them, but I'm returning the OBDII Adapter to Amazon because this was my only use for it.
Hope this helps!