low/no charging

No. You may have some aftermarket item, and may not even have the factory regulator. A photo would go a long way.

The field wire...early style on right only has one. It has a total of two wires. The big wire hooking to the nut/ stud is the output

The "push on" small wire is the field

The newer alternator on the left has TWO field wires. (Two "push on" connectors). You can use the new style in place of the old style by grounding either field and hooking your existing green field wire up to the remaining field terminal.