Did you ever figure this out? After I had my windshield replaced last year, I noticed that the compass on my mirror stopped working and will only show "100F" on the display, no matter what. I've followed the manual's instructions on how to set the zone, done resets, disconnected the battery, checked the cable connections. Nothing works. I would have gone back to the shop, but it was a few weeks later and I didnt want to be bothered with them (terrible shop) anyways. I'd like to fix this myself. If it's a simple as replacing the mirror with another from a salvageyard, I'd have no issue doing that. But just want to know if its absolutely the mirror thats the issue or is it something else? (another control module somewhere feeding info to the mirror?)