A fuse blows for only two reason
#1 short circuit which causes a higher current draw than the fuse is capable of handling,
Look for chaffed or broken wires rubbing on metal parts, (ground)
#2 overload of the circuit, if current exceeds the amp rating of the fuse it will blow, was any accessories added to this circuit? Sometimes a defective bulb can cause this, in the case of electric motors tight bearings can cause higher current draws.
Somtimes looking at a fuse closeup will give you a indication of either 1 or 2 above.
In the case of a short circuit the fuse will blow instantly somtimes leaving black residue on the part of the fuse where you can see the element. In the case of #2 the element of the fuse would have just opened.