Ducati ST4s Owner's Manual page 152

The fuse located on a side of the battery (fig. 50.2)
protects the electronic regulator. Remove the fuse cap (2)
to expose it.
A blown fuse is identified by the interrupted inner
filament (3, fig. 50.3).
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.
74
3
IN GOOD CONDITION
2
fig. 50.2
3
BLOWN
fig. 50.3