Just wanted to add an update here to see if anyone has any suggestions. So I've managed to obtain a wiring diagram and factory mirror harness pinout from my service advisor at the dealer, see attached. I'm still trying to get the message center to stop giving me the compass missing warning every time I start the vehicle. It looks like pins 2 and 6 are for the compass. So far I've tried connecting them with a 100, 1k, 10k, 1MEG ohm resistors and no luck. Bravely, I took it a step further and also connected 2 to 10 (ground), then 6 to 10 with all the same loads, still no go. I also, ditched the resistor theory, and shorted 2 and 6 with no luck still. I suppose I could try something much smaller like 10 or 20 ohms, will have to obtain. Just wondering if anyone has any experience attempting this...
Oh, yes, just FYI, dealer has confirmed there is no disabler flag in the programming to silence this message btw, which is why I'm still chasing this.