Ducati 999 2003 Manuel D'utilisation Et Entretien page 134

Tank filler plug (fig. 29)
Opening
Lift the protection lid (1) and fit the ignition key into the
lock. Turn the key clockwise 1/4 turn to unlock.
Lift the plug.
Closing
Refit the plug with the key in it and push it down into its
seat. Turn the key anticlockwise to its initial position and
take it out. Close the lock protection lid (1).
Note
The plug can only be closed with the key in.
Warning
Always make sure you have properly refitted (see
page 54) and closed the plug after each refueling.
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1
E
fig. 29
35