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 looking backwards through the mirror, detecting headlights of following cars. When the ambient light sensor thinks it is night, the second sensor will cause the mirror to dim if bright enough lights are detected.

However, at my latitude (60N) we have extended dawn and dusk periods and very often the ambient sensor thinks it is day so no dimming occurs, while I am still very much annoyed by the glare from following cars. There is no built-in manual override, so it becomes an issue.

The solution to this problem is to trick the ambient light sensor into believing it is night, as presented in https://www.thingiverse.com/thing:2889660 . I had some issues printing it, so I designed my own version from scratch as shown here, this one prints lying flat on the bed.

The main "frame" part is glued together using either superglue or thin double adhesive tape. Before gluing, insert the slider piece. When correctly assembled the slider will not fall out.

The parts are designed with tolerances requiring them to be printed with 0.2mm layers and 0.2mm extrusion width, or less. If you live in a hot climate you may need to use ABS, but I have used PLA with no issues.

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