Article by sifty of the XLFORUM ¹⁾

Some simple diagnostic tests can be done with a multimeter.
Note, these tests should be performed after the initial visual inspection and cleaning as outlined in the service manuals.
And so are based on testing the unit out of the bike.
The results of these tests should determine if anything is seriously wrong.
But will not identify an intermittent generator fault,
(these can be hard to diagnose, and probably need testing on the bike so the genny can be driven at varying revs).