Ducati ST4S ABS Owner's Manual page 84

The fuse located on a side of the battery (fig. 83) protects
the electronic regulator. Remove the fuse cap (4) to
expose it.
A blown fuse is identified by the interrupted inner
filament (5, fig. 84).
Important
Switch the ignition key to OFF before replacing
the fuse to avoid possible short circuits.
E
Warning
Never use a fuse with a rating other than specified.
Failure to observe this rule may damage the electric
system or even lead to fire.
84
5
IN GOOD CONDITION
4
fig. 83
5
BLOWN
fig. 84