I'm sure I know less about wiring and electrical systems than most on this
list, but these videos from Jamestown Distributors explained some basic
concepts that I didn't know.  Jamestown Distributors sells boating stuff,
so the videos are not specifically related to vanagons or wheeled vehicles
for that matter, but it certainly wouldn't hurt if we repaired and
maintained our electrical systems by nautical standards.

https://www.youtube.com/watch?v=tUul6kB9slo

https://www.youtube.com/watch?v=GETAtxWuDxA

https://www.youtube.com/watch?v=Zd8af95HK68