Has anybody tried installing an auto-dimming mirror from some OEM? I was looking on ebay and they seem to be reasonably priced and easy to install. Some even come with compasses and thermometers. I'd try to find one with a red display. I've always wanted a thermometer in the car, and this way I could get a compass and auto dimming mirror too!

 

I doubt they need anything other than power and ground. Attachment method could be the other issue. Most of the ones that I've seen have been quite a bit bigger than a Miata mirror though. The stock mirror already takes up a fair percentage of the view area for me.

 

This is relevant to my interests. I want to mount an auto-dimming mirror to my dash so that I can see something besides rollbar behind me. Temperature readout would be a bonus, but it seems that would have to be read upside down.