I think what you should have is 2 6 pin connectors on either mirror loom, these are joined together with another loom that goes inside the car between the 2 holes in the doors, and has 3 wires that connect inside the car, an earth a live and the wire that connects to the heated rear window switch:
[]-----*---------|---*-----[]
|
|----------1
|----------2
|----------3
[] = mirror
* = 6 pin connector
1 = live wire
2 = earth wire
3 = heated glass wire
My 'full loom' only came with 1x 6 pin connector for the drivers side, the passenger side was just cut and I have no loom from inside the car!