I know people have added auto dimming mirrors, but not sure about OEM route. I can tell you that the harness is part of the headliner harness which runs down the A Pillar to the driver kick panel fuse box. On mine there’s 2 connectors that come down. 1 that connects to something by the footwell, and the othe the fuse panel. Not sure which one is for the mirror, but the harness is definitely 1 piece for the whole headliner.
My guess is if you want the OEM auto dimming harness, you’re either going to have to buy the entire headliner harness, which is probably in the hundreds if not 1000s. Or you could hit up a junkyard and maybe pick up an entire headliner for a 100 with the harness. Or maybe you can get a pigtail with the connector from the junkyard if you’re lucky. I certainly wouldn’t recommend dropping the headliner to do this.
Or you can look at this thread. May even be universal...
Instal of Auto-dim Rear-View mirror (Gentex)