Bill,
there is a switch valve mounted to the fan motor that hooks to to thermo/wax valve. The thermo/wax valve controls the fan speed as the coolant heats up. I believe it restricts the fluid, forcing it through the fan motor, spinning fan faster, to increase cooling. Don’t really know the function of switch valve, other than a bypass to return fluid back to system reservoir. The thermo/wax valve is mounted in the radiator, look for two smaller hydraulic lines running to thermo/wax valve. Hope this helps.