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 devicesRectifier-regulator
The rectifier (1) is placed in the electrical components compartment.
The rectifier/regulator consists of an aluminium casing containing the diodes
that rectify the current produced by the
alternator. It also contains an electronic device that regulates the current
supplied by the alternator ...
Refitting the starter motor gear
Position the washer (20) and the gear (19) in the pin (21) and take the pin
into contact with the crankcase half.
...
Removal of the rear brake disc
Remove the rear eccentric hub (sec. 7 - 13, Removal of the rear wheel
eccentric hub and rear wheel shaft).
Undo and remove the four fixing screws (13) of the brake disk to the wheel axle
and remove the rear brake disk (14).
Loosen the four screws (24) and remove the rear phonic wheel (25). ...