Hi mate,
mirror will work fine with just the +ve (white) and -ve (black) connected..
If you want the dome and reverse inhibit functions then you need to connect the grey wire to a feed that goes live when the car is in reverse (reverse light feed?) and the green wire to a feed that goes live when the interior light is on (interior light feed?)
Hope this makes sence??
As I said earlier, most folks doing this mod don't bother with either of the inhibit feeds and just leave them disconnected..