I suspect this post will sit, dead, but have gotten further than perhaps others stuck without a night mirror in their Model S. In post-AP Tesla's, the night mirror is not always active as I believe "photochromic" was a positive option of the tech package. It's a lame situation, as there is no manual flip for headlights from behind and Tesla refuses to fix it, or even be paid to fix it. They claim the mirror is part of the AP system, but it's made by Volvo. So, I'm going public with where I am, with a white flag for those who might have the access to know better. So far, -Inactive photochromic (night) mirrors become functional, if put in cars having the tech package. So, this isn't hardware. -A vertical 5-wire DIN plug feeds both. -Top two wires are steady 12v, for both functional and non-functional cars -middle wire is dead, or shows 1.3V with mirror activated by a light source in the car having the "photochromic" option -bottom two wires are dead, and open circuit (full resistance) with no light -with light, the two bottom wires form a circuit (zero ohms), if attached to the mirror when it receives light. You begin to see resistance return as the light goes away (light sensor is on the mirror glass side). I believe a closed circuit could be telling the car's controllers to send 1.3V to the middle wire, but haven't got the Tesla back end tools to know. So, the question for anyone with them (WK057, Ingineer...) is whether that is the case, and if the feedback coming from the mirror's closed circuit can lead to 1.3V, instead of 0V, coming back from the car? There's another way to do this, by perhaps coming up with a 1.3V source, but that would be a mechanical hack (maybe a AA battery). I'm leaving this riddle to seek a bit of help, and maybe help anyone else perplexed by how their ~100k car ended up without even a flip mirror... Almost there... Thx.