90 Dodge 350 15 pass van not charging, alt checks good.. volt reg? where? or?

What is your question?

suspicious 2x3" metal "can" on firewall front connects to batt..but no voltage on any of the other 3 wires? Saw post about engine control circuit inside firewall? in engine comp't? under dash? inculding regulator? what does it look like? Dies when either batt cable pulled. Any other parts in charging system? Heard that cables loose to dash voltmeter could be the problem? This is my home electric generator w/big deep cycle batt & inverters. Any other quick diagnostic tests? 12V to ground on all 3 alt terminals OK. Connectors cleaned/replaced. Multipin plug in wiring on front of firewall kills engine when unplugged.