Please describe how you tested the Blower Motor to consider it Good. They can get dirt in the brush holders. Then the brush springs can't keep them pushed against the commutator segments as the brushes wear. Sometimes if you put the motor in one position it'll run and it won't run in others. I've heard of removing the motor and tapping it on a hard surface in various directions to shake the dirt loose. It may run awhile, but the dirt's still there and will usually lock the brushes again.
Have you checked for voltage at the motor terminal and the resistor block? Tried a different fuse? Is the blower motor grounded somewhere? If it's a single terminal for the hot lead, the motor needs a ground somewhere. If the plenum it's mounted to is steel, probably OK, just snug the screws. If the plenum's plastic, run a ground wire from the motor shell to a known good ground. See if anything changes.
