Ducati MONSTER S4R Manuel D'utilisation Et Entretien page 131

Replace the bulb (4, fig. 54).
Notes
Be careful to hold the new bulb at the base only.
Never touch the transparent body with your fingers or it
will blacken resulting in reduced brightness.
Fit the tabs at the base of the bulb into the corresponding
slots to ensure it is correctly oriented;
engage the end of the clip (3, fig. 53) with the mount in the
headlight body. Reconnect the cables.
E
To replace the parking light bulb, detach its connector.
The bulb (5, fig. 55) is of the bayonet-type: press and twist
counter-clockwise to remove. Change the bulb and refit by
pressing and turning clockwise until it locates into its seat
with an audible click. Reinstall the connector and secure
the surround/reflector assembly.
54
4
5
fig. 54
fig. 55