sub'd. Never even knew about these mirrors. The dim when headlights hit them/at night?

 

I don't know about the side mirrors, but the rearview has two photocell looking things, one on the non-mirror (front from the car's perspective, back from the mirror's perspective) side, plus a similar looking one at the top/center of the mirror. There's also a LED alongside the dimmer button. I'm guessing that is to indicate whether auto-dimming is activated?

 

On my 1998 SC400 my side mirrors don't dim out, I actually found that annoying like how the rearview mirror does (you get used to it) then all of a sudden the same car has bright lights on the side mirrors.

 

I swapped it in today. Haven't tested it yet, but while looking for clarification of what the button does (does it lock in dim mode or enable auto-dimming?), I used different search words than before and found several threads stating that the '96-00 auto-dimming rearview mirrors are indeed backward compatible.

https://www.clublexus.com/forums/sc-...k-in-92-a.html
https://www.clublexus.com/forums/sc-...uestion-2.html

Edit: I tried it out tonight and it's pretty cool! I only had a couple cars behind me throughout the drive, so not much opportunity to test how fast it adjusts both directions, but it seemed quite quick to auto-dim. The LED is a very faint green, so it doesn't annoy you when lit. I assume it indicates that auto-dim is enabled.