Hello Makem,Ok then. There is no schematic diagram in the instructions but, working it out I can see the solution.
You need the twin wire cable "C" from the towbar wiring kit. This runs fromfront to rear, inside the car and has a thick red and a thin, yellow/brown. It costs about £15.00.
At the top of the drivers kick paneland adjacent to the throttle pedal are a pair of wires in an orange connector;a thick, brown/yellow, and a thin, brown/blue. The cable, "C" connects to this an runs under the door framelower trims/carpet. Insert a 20 amp fuse in fuse position F20 and there you are. 12v in the rear!! I actually solved my own problem as well whilst investigating your query.