[Michalb]

The exterior mirror gets power from the center rearview mirror, which may be the same circuit but I'm not confident about it. I definitely know that the circuit runs from the center mirror, to the driver door module, to the auto mirror, back to the module, and all the way back to the center rearview mirror.

I have had several issues with the driver auto mirror, being that I retrofitted it into my van meant I had pulled used parts from donor vehicles. I grabbed 3 of these mirrors, (with blind spot lamp), the first one wouldn't dim no matter what so I assume it failed prior to me grabbing it. The second turned dark one night and stayed dark since, even after removing it and waiting a few days. The 3'rd I grabbed is now installed and working fine but it will also fail. I replaced the mirrors completely for the 3'rd mirror, when i went to add blind spot. The mirror wouldn't dim and the blind spot indicator also intermittently worked. I removed the wire protection between the driver mirror and door module, and found that water had made it's way into the wires themselves and caused corrosion inside the wires which extended almost to the mirror connector on the door module. So I ran 4 separate wires into the mirror itself to regain the functions but I tapped them into the existing damaged wires, so whatever water was getting into the wires, will continue to do so and eventually will stop one or both functions. I'm upgrading to power folding so I'll be replacing the entire mirrors at a later date.

I don't think the overhead screens nor the radio produce enough light to cause the mirrors to dim. My mirrors dim when i put the van in the garage and it's daylight outside, the light the sensor sees is enough to dim it. My mirrors will also dim when I turn the interior lights on at night. Sounds like either a bad/intermittent circuit, or a failing center mirror. I just replaced a failed rearview mirror for someone which turned on the green light but wouldn't dim, they didn't have the driver side auto mirror.

You could probably just unplug the center mirror and run 3-10 volts through the day night + and - wires and see if it dims or not.

 

[Michalb]

There’s no sensor in driver’s side mirror. It’s all controlled by the center rearview mirror.
Yesterday I tested in the dark. When I had the ves screen playing something both mirrors were dark, closing the screen made the mirrors go back to normal. But before that and just before creating this thread it was not that dark outside yet for the front sensor and back sensor to have that high lighting difference to cause the mirrors to dim. Have to do some more testing I guess.

I'd say as long as it works, just leave it. Or keep an eye out, maybe it only happened the one time and never will again.