If for some reason you bought a Gentex 536 (GNTX-536) instead of the ever-so-popular Gentex 453 (GNTX-453), you will not be able to use the regular cable that all 453 model uses.
I thought all the Gentex 10 pin connectors are the same, they are not. The 536's cable is slightly different and pinned differently.
Basically I got a mirror off a Hyundai Genesis, because it had compass, and the previous Gentex 453 Homelink Auto-dimming mirror that I have did not have it.
You can source the car to mirror harness here:
tell them you have a Legacy, it should be $7 shipped.
If you bought a Gentex 453 you can stop here, it's plug and play.
It's a cable with three wires, 2 black ones, and 1 black with white stripe.
From my multi-meter reading, the black with white wires did not have any power, the center black wire is ground, the other black wire has 12v when the key is turned to either ACC or ON
Gentex 453 (Model: OBIHL3) Mirror has a wiring like follow
Gentex 536 (Model: ZTVHL3) has the wiring as below
4 wires total:
1 black wire - ground
1 yellow wire - my research says it's suppose to connect to the reverse light to disable the auto-dimming feature when you are reversing
1 pink wire -
1 pink w/black stripe -
The two pink wires powers the Auto-dimming feature, other powers the Homelink and compass feature.
What I did was
connect the two pink wires to the black power wire
ground to ground
yellow - left alone
bam, everything works, and now you can enjoy your Homelink/Auto-dimming/Compass mirror for much cheaper than the OEM Subaru ones for $200+
This thread might be helpful too.
Hopefully this will be useful for someone in the future