when do the heated mirrors work?
 

What activates the circuit for the heated mirrors (92 300D)? The manual mentions that they operate at "low ambient temps." Does this mean it looks to the outside temp sensor for a signal?

Thanks!

I dont know how MB does it, but it is triggered by the rear defrost or the heated seats in most cars.

Hmmm... well mine are on at all times, but I don't have heated seats and the rear defrost is not on. My temp sensor is bad, though, and shows under freezing at all times. I thought maybe that was the problem. I have a different (known good) sensor to try, so maybe that'll help!

For the w201, there's a thermostat on the back of each mirror (see attached service manual section). Maybe yours is similar?

Each mirror has a thermostat/switch stuck to the back of it.

Hard to tell when they're working without an ammeter.

Thanks guys... I'll keep investigating! (They are definitely working, though -- or one is, anyway. It's very warm on cool days!)