^^correct sir the wiring in the mirror isn't there. Since Subaru doesn't service all the parts inside the mirror it is not available.
You have a couple options:
Rig it up yourself, you can run wires into the mirror, figure out some generic terminals to hook to the LED units, and then tap the wires on the door side mirror plug. Check this similar DIY
for 08-10 WRX for an idea of what to do there.
Get the original wiring and add it (PM me and I can set you up with signals/caps/wires) you can add the signal wiring into your mirror it will be like stock, plug for LED unit on one side, snaps into the mirror plug on the other. You can use my JDM mirror DIY
to see how to disassemble the mirrors to add the wiring.
What's nice is all the 11+ WRX have the live signal wires, so you just need to add it to the mirror and it will work.
I really need to make an FAQ for this...