On a roll after getting my aux. heater to work I thought I would have a go at figuring out the heated mirror switch. My van is an Aclass Pilote on a h Mercedes base so I does not have the standard mirrors, switches or heaters. The rotary heater switch next to the mirror adjustment switch has four positions, each of which I have tried and each warms the mirrors (photo below). I have had the van from new (nine years) and never been able to suss this out and have put up with warm mirrors even in the middle of summer, anyone any idea how to turn the heater off?.