|Guzzi Charging System Reference
I rode Boxer BMWs for about 30 years and had to struggle with their shaky systems. Now I have a 84 V65C and found that is has almost the exact same system as the old BMWs. There is a great and inexpensive manual to help with the testing and troubleshooting of these systems.
Classic Boxer Charging
Self Help for the Electrically Challenged By Rick Jones
Hope this helps