Originally Posted by
Wiscon_Mark
If Subaru is still making them the way they used to, yes, likely the wiring is already there.
It should be easy for you (or the dealer for that matter - they should want to make a sale to you) to tell as the mirrors are on the doors. Just pop open the inside door trim and see if there's a harness plug unused right by the mirror.
Short of that, my experience with OE accessories is that they come with everything you need (aside from tools). So have them pop open a box for the kit and see how much wiring harness is included.