Have been following all info in this thread as I have the same problems with my 1999 Focus heater blower circuit.

Currently have replaced the thermal fuse (with Maplin component for £0.82p) but still no joy. Now suspect the switch is at fault but have yet to access it - reckon I need to remove the radio in order to get at the rear of the panel from the inside, where I can start tracing resistances from the switch terminals back through the resistor pack.

Incidentally, having removed the blower motor I have established it's at least functioning ok in itself by turning the ignition so all electrics are on, with the motor unit connected and sitting on the floor of the footwell, and then holding it tight whilst shorting the black/red wire on the heater motor connector to chassis ground using a length of very thick insulated wire (from a mains twin and earth cable). Motor practically jumped out of my hand and there was a nice spark where I was touching my insulated cable to the black/red wire connector, but at least now I know the motor actually still functions.

I found the following wiring diagram from another related forum which helped me work out how to do the above.... maybe others here will find it useful:=.

If anyone's got any advice as to how to go about removing the radio and accessing the rear of the heater blower switch on the dashboard, please let me know.

Cheers