I bought a new replacement tailgate cable for mine -- the part that you're unplugging that goes into the tailgate to the factory camera.
Then got the wiring diagram and got the pin-out of each pin. Pretty straight forward - pos/gnd, video pos/gnd, and a continuity trigger (the wire that tells you that irritating "the camera is disconnected, call your dealer" on the monitor).
Now, for my year of cable, that Ford PN is DC3Z-14A412-A. May or may not be the same for yours, do a little google'ing. It was $14.95. This plugs into where your factory camera just got unplugged from.
Then I simply connected it to a basic generic backup camera, $20.
This is where I found the most helpful info
here on The Diesel Stop
