Boxerworks.com

And what voltage regulator do you have ? The original tin can version came with points and all sorts of internal mechanisms that can break, hangup and/or get dirty. Highly suggest you try a new regulator. The newest ones are all electronic. The best have adjustments so you can dial in your charge voltage. This is necessary since sealed AGM type batteries like a higher charge rate than the old "flooded cell" type batteries.

http://motoelekt.com/charging.htm

The $39 from Rick James is the best I've seen of this class.

What do you think about theses?

non-adjustable - set to 14.3v ($19 plus shipping)
https://www.euromotoelectrics.com/product-p/vr-ext.htm

or this adjustable one ($25 plus shipping)
https://www.euromotoelectrics.com/produ ... extadj.htm

Once on the road on my Guzzi 850, (same Bosch charging system) my rotor failed, and the bike stopped charging. I got to a dealer that had a rotor in stock and they installed it. They asked if I wanted new brushes installed. I went for it. During the installation of the brushes they somehow (pushing down with a screwdriver?) managed to damage the base of the brush where it attached (soldered) to the wire. So the bike would sometimes charge, and then quit charging if I hit a bump, or just for no reason. Took a while to figure out the problem as it wasn't an easily visible fault. The sent me a new set of brushes, yea, thanx

I finally think I found out my problem, It was similar situation with light intermittently coming on. Low charge rate as well. I discovered a broken rubber mount on the diode board (upper left corner), and overheated looking ground wires. I put in solid mounts, but had no output from the board. Grounding grommets look slightly corroded, and PCB material around the ground posts broken on both sides. New diode board will be needed.
I am thinking about re-locating the diode board to behind the battery.