If its really a Sporting there should be three cables. One goes in to the top of the box right behind the reverse light switch. It will not go in with the reverse light switch in place, you have to take the switch out, fit the cable, then refit the switch.
It could also be that the cable has come off the gearknob. Thats an easy one to check by opening the gaiter and checking that the outer part moves down when you press the knob down.
Cheers
D