Hi David,
Welcome to the forum.
To answer your question, the following possibilities come to mind.
1. The fan motor is tight in its bearings, and hence drawing too high a current.
2. The connector has been damaged by overheating, possibly due to the above.
3. The replacement resistor was defective, or of inadequate quality.
It is worth noting that the cab fan motor is one of the higher loads supplied by the electrical system, and that the heating effect of an electric current is proportional to the square of the current.
