Surely you can just buy the looms needed and chop and change, would no doubt work out alot easier...but iirc my heated mirrors worked through the rear window switch

 

I am sure that heated mirrors on the zr and zs are on all the time

Sure you could wire into the rear window wiring if you wanted steve, no sure how but would imagine it would be just as easy to wire them up so the whole unit works as it should......that is making little sense to me lol, but i know what i mean

 

the thing is the Rover loom was totally differnet to the MG loom for the central locking, no loom there for the electric windows/mirrors so i had to "retro Fit" the electric windows if you know what i mean, so all i want to do is run a wire from the heated rear window to the "new" mirrors, all i want to know is, is this possible and does anybody know what wires behind the dash to splice into

 

can only guess at this mate, but i would say pull out the switch and there should be 3 or 4 wires goin into it..1 or 2 for the lighting of the switch and 2 for going an heating up window, these would be the thickers ones so splicing into them should suffice. Could be totally wrong as it's been a long time since i seen the wiring going into one of them switches but should set you on right track...hopefully

 

Cheers

 

should be fine since the rear heater is fused

 

why bother, they burn them selves out in no time at all then you'll be replacing the mirror glass every winter.