Ducati ST4S Owner's Manual page 62

Disassembly
R.h. low beam bulb:
remove the rubber cover. Press the lower quick-release
button to disconnect the connector (1, fig. 64).
L.h. high beam bulb (fig. 65):
disconnect the connector of the white bulb cable from
the front wiring. Remove the rubber cover from the
headlamp body and pull out the bulb cable.
E
Note
The black ground cable connector does not need to
be disconnected to replace the headlamp bulbs.
Release the clip (3) that secures the bulb and remove it
from the socket (fig. 64 and 65).
Replace the bulb.
Note
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 bulb brilliancy.
62
BLACK
1
3
3
3
fig. 64
WHITE
fig. 65