So I just installed a Gentex K2a Auto Dimming Mirror 79$ shipped from Amazon on my 12' Focus. Install took around 45minutes. I snaked 2 tiny wires around the passenger side headliner, then around the a-frame plastic under the airbag, and down the passenger side weather stripping to the fuse box below the glove box. There is a vertical bolt attached to the frame to the left front of the fuse box if you look up and the circle connector on the wiring fit the bolt perfectly to use for the grounding wire. Then I used an Add a Fuse on Fuse #85 which is a 7.5a fuse to attach the 12v wire(bare in mind the auto dimming mirror draws very little power). Attached mirror, plugged it in, and it works perfect.
Btw, the auto dimming mirror directions wanted me to use a vampire connector on a 12v wire but I decided add a fuse was the better route.