Wiring diagrams look like ancient Egyptian hieroglyphics to me. I'm gonna guess the grounding of the voltage regulator is likely. As I've been finding other corroded connections of late. I'll read the attached and check the grounding out. Thanks!
Try not to give up before you start.
You don't have to guess.
See what the ammter guage indicate. Does it change with rpm? and if you can measure voltage with a meter, that will help immensely.
40 amps through that circuit will start to overheat stuff.
Uncontrolled votlage can also sometimes damage things. Disconnect the AFR reader for now.