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 devicesSpark plugs replacement
Check the colour of the ceramic insulation around the central electrode:
an even, light brown colour indicates the engine is in good condition and
running at the right temperature.
Inspect the centre electrode for wear and check spark plug gap, which should be:
0.8+/-0.1 Mm.
Important
...
Checking the fuses
The main fuse box (1) and the secondary one (2) are located in the tool tray;
to reach the fuse box remove the seat as
specified under sect. 5 - 3 "Removal of the seat".
The fuses are accessed by removing the cover, which shows the ampere ratings and
mounting locations.
For ampere ratings ...
Noise and exhaust emission control
system information
Source of emissions
The combustion process produces carbon monoxide and
hydrocarbons. Control of hydrocarbons is very important
because under certain conditions, they react to form
photochemical smog when subjected to sunlight.
Carbon monoxide does not react in the same way, but is
toxic. Duca ...