MK4/B5/B5.5 Jetta/Golf and Passat auto dimming mirror harness. Harness includes 3 wires, ignition power to fuse 5, ground, and optional reverse light signal wire black/blue in bundle near hood release handle (so mirror undims when vehicle is backing up but this is not required for rest of mirror operation). Can be used on practically every VW/Audi auto dim mirror in the past 20 years including compass style mirrors that have 6 pin style connectors.
If you still need to source the mirror though, ensure your windshield has the proper mount for the mirror you want to run. For example mirrors with additional rain sensors use different mounts from manual dimming mirrors.