If you have 12V across the fuse, that means the fuse is bad. You should not have any voltage drop between the two sides of the fuse.
Can you get to the motor terminals? Once you get a good fuse in, I would check the voltage at the blower motor.
If you have power there, the issue is in the motor or its ground. If you don't, then move up to the switch amd check there.
Just keep moving up or down the circuit until you find where the power stops flowing.
