Try draining your battery then watch it while the engine is running..trying to put a charge back in it. That's when the gauge is most noticable
Ford ammeters. I have never seen a dash ammeter look like it is working. My 77 F100, 68 F100, 79 Bronco, 66 Mustang, 67 Mustang or 68 Mustang , Not a one of them ever appeared to work. What's up with that?