Not sure how to title this. So I recently bought and installed an auto dimming rear view mirror with homelink & compass on my 08 Legacy. I bought the mirror off eBay and so It's possible something is missing or maybe I'm just a derp. I can't figure out how the small black box that mounts off the post holds in place. I don't have anything it clips too. (Hopefully adding pictures below)
I never had the one off the windshield in my Legacy, but on the one in our Ford, the black plastic just snaps into place over the mirror's mount and there is nothing else that holds in into place (such as affixing it to the glass).