Apparently Ford put a resistor by the motor to protect the motor in the event the lock lever is held down and you try to unlock the door (child holding down lever). I found a website that indicated that you need to remove this resistor and take some aluminum foil, short the resistor and place back in. (In other words, foil the safety circuit).

Door locks stop working including the remotes. Doors would not unlock with the button or with the remotes that came with the truck.