I have no specialist knowledge or experience of vehicle electrics but...
The fuse is trying to tell you something...
When it blows it's saying that too much current is being drawn. Either you have a chafed wire shorting to earth (possible but very doubtful) or you have a problem of some sort with the motor.
Best case I would suspect the motor being lose and wobbly on its mountings and the wiper linkage jamming up - the motor stalling and a resulting high current causing the fuse to melt.
Alternatively the motor itself may have burnt out resulting in a short-circuit fault - that would cause the fuse to blow immediately if the wipers were selected to run.
Good luck...
Peccavi
December 2012