Suddenly, without warning, CJL exclaimed (14-Dec-05 10:43 PM):

I was once told (on this ng) that the blower motor itself could be
causing the resistor to go (overcharging?  I forget).  I'm on my third -
replaced the OEM, that died in under 11 months, replaced it again.
Knock wood, that one's holding, but if it breaks too, I'll be replacing
the motor.

I've a 2001 Dakota. Quite a common problem in this year's vehicles, from
what I've seen on this NG in the last couple of years.

jmc

What you need to do is check to see how much current the blower motor is
pulling.  If it has some shorted turns or a bad bearing, it will be pulling
excessive current which would overheat and burn out the resistor pack.

Replaced the resistor block and blower motor so far it has been working
fine.  The blower motor was hard to turn so I suspect that the grease in the
bearings had dried up causing the motor to pull more amps and blow the fuse
in the resistor block.

Hope this helps someone out.