Ducati ST4s Owner's Manual page 192

Turn indicators
The bulbs of the turn indicators are accessible after
removing the instrument panel side guards.
1
Front:
Turn the bulb holder (1, fig. 85) anticlockwise and remove
OPEN
it from indicator body. Withdraw the burnt-out bulb and
replace it.
Refit the bulb holder with the round slot pointing upward
and turn it clockwise until it locks in place in the indicator CLOSED E
body.
fig. 85
Rear:
remove the screw (2, fig. 86) and detach the glass (3)
2
from the indicator body holder.
A
The bulb is of the banjo-type: press and rotate anti-
clockwise to remove; fit the spare bulb by pressing and
3
turning clockwise until it clicks.
Refit the glass sliding the small tab (A) into the suitable
slot in the indicator body and tighten the screw (2).
fig. 86
83