It comes time to wire to this alternator wiring. I have a 97 impreza 2.2 with a 2 pin connector large white wire and a skinny black/white wire. The ea wiring has a large wire wire which I know is 12v and two other wires bigger black/white wire and a skinny white/red wire.

Do a search on the forum, I'm sure it's been covered on here somewhere. 

Otherwise the next best thing is to study the wiring diagrams of both vehicles to work out a solution. 

You'll probably find the small wire is ignition switched and reference wire - so you could tap that into the ECU's power wire so the alternator is triggered with ign ON.

but you have to confirm what that wire does first. 

Cheers

Bennie

dunno if it is going to help but on my 99 RX 2.0 Imprezza the two white wires both had charge voltage in them when running according to my mental notes made when engine was in and running

I ran little wire to little wire and big wire to big wire and its charging like it supposed to now