Originally Posted by Jeremy5848

The mirrors in the 124 are thermostatically controlled; the thermostat is supposed to close below 50F or 10C, more or less. The mirror, heater, and thermostat are all one unit. The thermostat is not separably replaceable.

Using padded pry tools, it's fairly easy to pop the mirror out of the housing, unplug the two-wire connector on the back of the mirror, and remove it to your bench. Put the mirror in your household freezer for awhile (or lay it in a pan of ice) and the thermostat should close. You can then apply 12 volts and the mirror face should warm up to the touch, until the thermostat warms up and opens. If you cannot get that to happen, then the thermostat is bad or the heater wires have failed open.

A new replacement is beau coup bucks, over CDN$100 at a dealer. I bought a spare for each side of my '87 from the local Pick and Pull for US$4 each because their computer doesn't differentiate between "mirror, glass only" and "mirror, Mercedes, heated, expensive."

See Spare mirrors -- good to have for pictures.

Jeremy