Hi, I had exactly the same problem where I bought a mirror 'On Line' which, if my memory is correct, had six wires but a connector that would have taken eight whereas the socket in the door had provision for twelve connections, but only six wires. I even went to my local Ford Main Dealer who told me that there was not any means of interconnecting the dis-similar components. Somebody did suggest going to a scrap yard and trying to make up my own interconnector, but to no avail. I tried to get a refund but was told it was too late, maybe you could try.

In the end I had to purchase the correct one through Ford Main Dealer appprox £130 !!
I don't believe there is a problem as to whether it is due to mirrors being heated or not, it is simply a case of Ford changing the connection format after the early Mk3 Galaxy, and the 'On Line' mirrors probably only suit the later Mk3 versions. The website I purchased from now state the mirrors only have the 6 wire connectors.