If the motor has an inrush current of 100 amps you don’t need a 100amp fuse. You need a fuse that is rated for its continuous load current but in a time delay style. Basically, there is a time delay built into the fuse. It will handle X amount of current for Y time. After that time Y has passed it will handle a continuous current of Z. There is no way to properly size the fuse without the inrush current curve for the fan and fuse characteristic curve. You may want to check the Ford manual from whatever car you got this from and see what size fuse and class that circuit is. I would suggest a 30amp fuse with a time delay. I would also meter the fan to see exactly what it pulls continuously. You wont be able to tell what its inrush current is with a normal meter so don’t bother. It happens so fast you will just see an erratic reading on your meter.
