Ammeter pegged...

You lost me at "I'm a mechanical engineer, but can't read a wiring diagram". Are you talking university-educated from an ABET school? (not U of Phoenix). In my BSME studies I learned op amp circuits, motors, control systems, even analog computers (long ago). Then lasers and such in grad schools. Anyway, great info here, so all it takes is the ability to read and process info (most people lack) and there are youtube's to teach basics. Some here try to trouble-shoot w/o a multimeter, even though you tell them "free at Harbor Freight". The main issue is lack of initiative for those that fail. For sure fix your over-charging problem before the dash cluster melts and the battery generates hydrogen (can explode).