The most likely cause is that the wire has fractured inside the rubber boot where it passes from the body into the tailgate. This is a common weak spot on most hatchbacks and estates, not just Fords.
I recently noticed the high-level brake light on the wife's estate wasn't working. This turned out to be a fracture and I found two other wires where the insulation had cracked and also the rear screenwash tubing was cracked in two places.
Not sure what you mean by 'front and back' - there aren't any on the front numberplate.