The fuse would blow because too much current passed through it. Either there is a short or the motor may have gotten bound up a little and sucked more current perhaps. Replace the fuse and see if it happens again. If it doesn't then leave it alone. If it repeatedly blows the fuse, then you have a problem.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record