Manual override for auto-dimming rear view mirror

UPDATE: After a couple of weeks of use I find it to work very well. Manual control of dimming of all 3 mirrors is restored when the automatic dimming does not work, which happens quite often. Every car should have one of these.

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I recently got a new car with an automatic rear view mirror dimmer. When it works, it dims all 3 mirrors which is fine. An automatic dimmer like this relies on 2 sensors, one ambient light sensor looking forward through the windshield and another sensor lookin