Ducati ST4s Owner's Manual page 139

Left switch (fig. 18.1-18.2)
1) Dip switch, light dip switch, two positions:
position = low beam on;
position = high beam on.
2) Switch = 3-position turn indicator:
centre position = OFF;
position = left turn;
position = right turn.
E To cancel turn indicators, push in once switch returns to
central position.
3) Button = warning horn.
4) Button = passing.
30
1
4
3
2
fig. 18.1