I don't have a port in the mirror, even though I have a GT premium. I tore it all apart yesterday, but didn't have a volt meter. Ford's wires are never consistent so I wasn't aware of which one was hot, so thought I would ask the group to see if anyone was aware.
I ended up hardwiring to a spare fuse in the panel. I tested the voltage from the USB and it was not enough to power the Radar Detector (Uniden R3). Also couldn’t find anything in the mirror, looked but not to hard.