Somewhere back there ^^^^^ I think I explained the fault tree of this problem.
Usually a badly fitted LHS Scuttle cover is not sealed to the windscreen. Ford supply a double sided adhesive foam strip to do this. If the seal, by foam seal or other bodge, isn't sealing, water drips down (through the pollen filter) into the top of the blower motor. Instead of spinning freely it only runs at a very slow speed. With reduced airflow across the resistors the thermal limit fuse in the pack fails.
If you only replace the pack, its not too long before it overheats again and the thermal fuse fails. You have to deal with the 'root' cause, not just the immediate cause.
1) Check the top cover and the pollen filter. Replace seals, clips, screws, pop rivets, etc.
2) Remove blower fan/motor from underneath. Carefully dismantle and free off bearings and lubricate, or replace with a good s/h one.
3) Now replace/repair resistor pack. A replacement thermal fuse from Maplin can be soldered in place costing just a few quid.
The other Martin