Ok, got a shell, saved a lot of money on installation by doing the wiring myself.
Problem is I don't know where to pickup power for the third brakelight.
The trailer plugs combine LH/RH turn signal and stop light power as do the stock tail lights, so that's out.
I suppose I could get it from the stock brakelight, except routing the wire to under the truck would be a pain (headliner removal?).

On second thought, I may do it this way unless someone comes up with an easier location.

 

On the '97 - '03 you could pick it up at the rear, not now! Ford garage wired mine and they had to run it under the truck to the engine compartment. Don't know where it hooked to.

 

Provided this info is a post a while back.... Not saying this is the correct answer but at least it is a suggestion. The lead for the high mounted brake light runs in the channel on the passenger side of the vehicle. I cannot remember the color of the lead but I think it is green. A test light with a shape tip will assist you in making that determination. The plastic step panel between the carpet and the painted area of the door seal can be removed by lifting it gently, you will see the harness in the tray beneath. I snaked 14 gauge wire surrounded by a 3/8” wire loom through the boxed frame and exited the wire at a hole in the frame that lined up perfectly with the tray. There are holes already in the tray so I just used one of them to get the new wire into the tray and to the brake light lead. Spliced the wires and reinstalled the step panel. Stop light lead that does not blink when turn signals activated accomplished.

Screwdrive