Ignore the idiot above his a troll, if he read he would have realized the problem had been diagnosed correctly by none other than yours truly

That is correct, however excess current is not being drawn, hence the fuse does not blow, the problem is heat, the resistor pack is what slows the fan speed, when you create resistance you also generate heat, which is what I suspect causes the switch to melt over a prolonged period.

I remember on the Mondeo this actually caused the wiring to heat up (not good) so much so that a good member who used to reside on here said there was a modified loom available.

Martin