TROVERMAN - the way it works as I understand it is, the windsheild washer fluid is heated with the engine coolant. the washer fluid heating coil is in paralel with the car interior or cabin heater/radiator. The auxiliary coolant pump, pumps coolant to both systems if the main water pump is not sufficient, I do not know how the auxiliary water pump is controlled, by what signal or trigger, is it from the RPM sender to the ambient temperature cotroller pushbutton unit?
The thermostat controls the flow of coolant in the washer reservoir coil. If the temp of washer fluid is below ~34C the thermostat is open and collant flow through the coil to warm it up and when the washer fluid temperature is over ~34C it stops the flow of coolant through the coil. In my case the thermostat was always open and sometimes the washer fluid would boil.