I'm glad yours is fixed and working. But there will be another owner with a challenge, so I hope this thread helps them too.
Just how one learns - and then teaches - the troubleshooting of electrical systems is still a mystery to me. I'm hoping to learn that art myself someday.
As for diagnostic charts - the ones that I have seen are either too simple to be useful, or are so complex they only work with the particular circuit they were designed for. There is really no chart that can substitute for a basic understanding of how charging circuits work.
By the way.....VOMs do vary in quality. Might as well get a good one. A good one - like a Fluke - will always have a way to tell AC from DC before the wrong assumption damages the meter.
When learning, I found it helpful to build up that basic understanding by realizing that all of the various motor/generator/battery systems are doing the same thing, and they do it in pretty much the same way.
Luckily, they all have only a small handful of similar parts connected up to accomplish the same simple goal - which is simply keeping a battery charged.
The only real difference being in a few details. With a little practice and study you will figure them out.
Don't be shy to ask dumb questions when you come to a mental roadblock.... Doing that sure helped me to learn this stuff.