Was the fuel pump assembly ever replaced with a cheap aftermarket one?
The only thing that would keep it from filling up is if it were full. It may keep trying to click off if there was some kind of vent tube blockage issue but you would still be able to pump it full, just at slower rate.
My long gone 2001 Sport Trac had a cheap fuel pump that broke the welds for the pump and sender bracket and it then dangled/floated higher in the tank. It would stop pulling fuel and run dry with about 1/2 tank of gas in it so I had to keep it above that level. My guess is that this is what's happening with yours.
You may need a new pump housing/carrier: 1993 FORD MUSTANG 2.3L L4 Fuel Pump & Housing Assembly | RockAuto
Delphi is going to be your best option for quality.