See
http://www.fordforums.com.au/showthr...56#post5302456
We now know there are two different types of fan speed controller; the more common (and more frequently failing ones) with the TO-3 Motorola transistor and seeming less common and less troublesome (no case in the vent to corrode) Bosch Blower Module ones. I suspect they are interchangeable but someone will have to trial test and see.