Just for anyone else, i did this on my 98 Ex (uk spec)
Just done this and took me 40 minutes (20 minutes trying to find the bolts i dropped!)
The replacement part in the UK is Ford part number: F4597402
1. Remove the two 8mm bolts that go into the right hand inner wing on this unit (speed control servo ?) then lift it up slightly as theres a tongue at the bottom that slides into a slott in the inner wing.
2. Unplug the power lead to the bottom of the speed control unit and move the unit away from where your working.
3. Remove the 8mm bolt (mines now a screw as i dropped it putting it back in!!!) from the clip thats holding the 2 metal pipes (you can then move these over slighty to get more room, only 10mm or so but its enough)
4. Unplug the blower elctrical plug (again this just gives you a bit more room to work in)
5.The item below is what your trying to get to (use the 2 metal tubes bracket for reference)
6. The blower resistor is held in by to 8mm bolts,(see below) remove these scres, i took the one on the left out first as it was harder to get to.
7. I also used one of these which was invaluble, however if you dont have one then a 1/4 ratchet drive with a small extension and 8mm socket on the end should be fine.
8.Leave the electrical plug connected untill you have the resistor out as there are 2 plastic clips holding it in, one on the top and one on the bottom that you cant get to till its out! It took a couple of minutes to wobble it free due to the rust on the contacts (see below)
9. As you can see from the picture, THIS is the problem, the contacts get rusty on the plug, i used a small flat bladed screwdriver to remove some of the rust till i saw bare metal on the plug and then plugged the new resistor unit it.
10. Fit everything back in reverse order!, mine now works on all 4 speed settings
I dont know if the resistor was actually faulty or if it was just the rusty contacts that were causing the problem, what you could do is just unplug the electrical plug and try clean the contacts on both the plug and the resistor unit however it will be difficult getting to the resistor contacts without removing it and for the sake of 6 quid its worth putting a new one in i though!
Hope the above helps.