On my 85 190E the switch is located on the front left (driver's) side of the cylinder head. If I remember it is just aft of the thermostat housing. Mine had three connections on the switch but only two wires. The parts man said most have two connections. There is no relay in the circuit. Removeing the connector from the switch and shorting the two wires should engage the clutch and if the motor is running spin the fan.

I just replaced mine a month ago. I'd give you the cost and part number, but my son has the car with all of the receipts in it.