Heated side mirrors - added (used), how to make them work?

You may need a different Rear Window Defogger Switch. I just looked on Subarupartsonline website for my MY 2001. And there are 2 different switches and one is W/O Heated mirrors and one is W Heated Mirrors. But it is not clear if that means changing the switch will make your heated mirrors work or not as it is not clear if there is a different harness needed as well as the switch.


Added: I also have a subscription with Alldatadiy.com and they also list 2 different switches for my Rear Defogger Switches depending on with or without Heated Mirrors.

I did find wiring diagrams on AlldataDIY, but the it is not clear about how the work.
The main problem is routed through the BCM on modern cars. Even the simplest of operations are run by the BCM.
I'll look into the switch to see, but don't see how that would work.
I'm thinking it may be something that needs to be "turned on" at the dealer.

Anybody know for sure how I can get the heat to work on these mirrors?