Ducati Diavel Owner's Manual page 124

Refitting the seat
E
Make sure all parts are correctly arranged and secured in the
underseat compartment. Insert the mounts (4) of the seat
base in the projecting parts (5) of the frame, then push the
rear end of the seat until you hear the bolt in the lock click
5
into place. Make sure that the seat is firmly secured to the
frame and remove the key from the lock.
4
fig. 109
123