The washer fluid is heated by coolant flow through a coil in the washer fluid tank, the temperature is regulated by a mechanical thermostat inline with the coil and located inside the tank, its a black device about 3" long. They fail and allow continuios heated coolant flow evaporating washer fluid.

The nozzles are electricly heated and the hoses are electrically heated, they are controled by an electronic thermostat which is located in the hood's rear cross brace underside on the drivers side on the 126 chassis I'm pretty sure. The thermostat is a black plastic rectangle about 1" X 3" long that snaps into an opening in the cross member.