One source says its up with the Blower Fan accessible thru Firewall another says up under the drivers foot well accessible after removing the fabric panel and under covering and is the smallish visible blue block with wires plugged in to the end. I have the car into a BMW shop this Wednesday and if i need to get the resistor thru the firewall behind the Expansion tank I'd like to do it there where he can drain , flush and refill the coolant. May have that done anyway as another shop recco'ed based on mileage i replace the T-Stat and the coolant does have about 40K on it.