The negative cable, which is normally connected to the negative pole of the battery, is fastened to the crankcase. From here, the cable branches off and splits up within the electrical system to carry the ground connection to the different elements in the system.

The image shows the ground connection on left side of the engine crankcase.
The battery charging circuit and power distribution
Electrical power for lighting and signalling devicesIdentification data
All ducati motorcycles have two identification numbers, for
frame (fig. 1) And engine (fig. 2).
Note
These numbers indicate the motorcycle model and
should be quoted when ordering spare parts.
...
Refitting the alternator-side crankcase cover
Before the assembly make sure that the water pump unit is fitted on the
generator cover (sect. 9 - 3.3, Refitting the
water pump).
If bearing (27) has been removed, lubricate its seat with specified grease to
fit it on the generator cover (13).
Fit bearing completely in its seat and orien ...
Removing of the rear brake control
Warning
The brake master cylinder manufacturer advises against servicing the
brake master cylinder due to the safety critical
nature of this component.
Incorrect overhaul can endanger the rider and passenger.
Maintenance operations on these units are limited to renewal of the following
par ...