most fords have a contact panel on the bootlid which contacts with a pin when the boot door is shut check that this connection isnt dirty or slightly corroded.
or rather than having a contact panel the wires to the motor may go through a 'concertina' rubber tube somewhere near the hinges. The wire may have broken in this tube due to the opening/shutting of the tailgate over time fatiguing it. This happened on one of Escorts once.