If the ammeter shows a discharge, is is discharging. Time to trouble shoot the charging circuit. As to the seatbelt interlock, if you trace the wiring from the seatbelt relay (the one with the bypass button) you'll find all it does is add another layer of control to the starter relay. On my '74 I just pulled the plug from the seatbelt relay and jumpered the two wires that go to the starter relay at the plug.
"We live in a time when intelligent people are being silenced so that stupid people won't be offended".
