At the rear, you should have two sockets with flip-top covers, one on either side of the hitch receiver. One is a flat 4 pin socket, one is a round 7 pin socket.
If there is no 7 pin socket, you do not have the heavy duty towing package. The seven pin socket gives you electrical connections for your travel trailer:
*left turn
*right turn
*left brake
*right brake
*running lights
*- 12v dc (electrical return, i.e., ground)
*+ 12vdc (hot line so the trailer mfr can do stuff like charge batteries, etc.)
If you do not have this connector, it's a PITA to add it.
The connector to mate a brake controller is under the dash, up in the wiring rats nest, and pretty close to just above the steering column. It's a socket that is factory wired into the wiring harness. I found it easily when I installed my Prodigy P3. The hardest part was cranking my aging bod on its side under the dash!
That socket is where you plug in your Prodigy (or other brand) brake controller for your travel trailer. As far as I know, Ford includes that socket on every Expedition because it's so cheap to provide, and including it means they do not have to have two different wiring harnesses during manufacture. Less inventory...
But if you do not have the heavy duty towing package, the cost to change stuff out to upgrade is far more than it would cost to simply sell the existing Expy and buy a factory-equipped model. Brakes, rotors, HD tranny cooler, HD oil cooler, HD radiator, that 7 pin wiring and the connector, and on and on. And even then, the frame will not be as strong--I was told the 4wd and towing package frames are somewhat stronger in critical places..
