Let's get a grip, everyone. "bad contact on fuse is causing high current flow to fill the need, same as bad grounding" makes no sense from an electrical standpoint.
Ohm's Law: Voltage = Current * Resistance. And Power = Voltage * Current.
A bad contact at the fuse will cause heat at that contact due to the resistance there with current flowing through it = power dissipated in the contact.
A bad ground will have voltage drop between it and the actual ground (chassis, usually). So there will be less voltage available for the connected device. With any load (resistive or DC brush motor) that device will draw LESS current, not more. It will cause heating at the bad ground terminal due to the drop there. It will NOT cause a fuse in the battery feed to heat up!
Chris142 is quite right. Brush-type motors with very worn bearings, brushes or commutators tend to draw more current then designed. Here is an example: the BMW E34 (5-series from '89-'95) is notorious for this. The stock blower fuse is 30 amps, and the HVAC blower normally pulls about 10 amps on high speed (with a somewhat higher starting surge, 17 amps IIRC). As the blower wears it starts to pull more current, but usually not enough to blow the fuse. Unfortunately someone did not design heavy enough wires, and the wiring harness sometimes
catches fire under the dash and burns the car to the ground!
The very first thing anyone should do when acquiring an E34 is to put a 20 amp fuse in that slot. And replace the blower if the fuse ever blows.
Now I haven't checked the wiring diagrams to see if our trucks feed the HVAC blower throught the fuse in question, but if so it's a legit explanation.