Ducati Monster S4RS Owner's Manual page 129

Fit a new bulb (4, fig. 52).
Notes
Do not touch the transparent part of the bulb with
your fingers, this will darken it and cause a loss of
brightness.
Insert the tabs on the bulb base into the corresponding
E
slots in the bulb housing to ensure the bulb is correctly
positioned;
hook the end of the clip (3, fig. 51) on to the headlight
mountings. Reconnect the wiring.
To replace the parking light bulb, detach its wiring
connector. The bulb (5, fig. 53) is of the bayonet type:
press it in and turn it anti-clockwise to remove it. Push the
new bulb in and turn it clockwise until it clicks into place.
Reconnect the wiring connector and replace the lens/
reflector assembly.
54
4
5
fig. 52
fig. 53