Hi Ry
From the problems you have listed it sound as if there is a break in the wire to the heated rear window/electrics in the tailgate (opening and closing tailgate over many years - wire fatigue) These wires are encased in a protective rubber tube between the tailgate and the roof of the car. If you can pull back the tube and feel/look at the wiring you should find the break. Disconnect the battery prior to working on the electrics and make sure you have radio and alarm codes prior to disconnecting the battery.
OR go and find an auto electrician
Good luck
Maurice
March 2009