Freelander 2003 Rear Window Problem.

Went food shopping this morning and with boxes and bags stuffed into the rear I shut the Rear Door(Well I think I shut it) because on the way back home I switched the heated Rear window on and it didn"t work.
When we got home I couldn"t open the rear door. I heard it unlock and the window came down a little bit then stopped but I couldn"t open the door. Tried shutting it and locking and then unlocking and the car unlocked and again the window came down a little bit and stopped again.so my Wife got in the car and pressed the Rear Window Heater switch and lo and behold I was able to open the Tailgate. When the car was empty I locked it then unlocked it but again the window came down a little bit and stopped the the door from opening so we tried the rear window heater switch and I was able to open the door again!!!!.Any Ideas?

A guess would be bad earth or some cable damage.
Poss it is earthing through the heated window when on.
I'm sure someone will know control unit location. Time to get the meter out.