Over the last four years, I have had to replace the fuel pump in my Mustang three times. And this most recent crap-out...no, it's not because the tank was close to empty. All these failures...obviously there's something else going on. Any ideas what it could be?
What brand of fuel pump are you using? A Ford replacement or aftermarket made in China? Most after market parts come from China (cheap junk). Running the fuel tank below 1/4 capacity tends to cause the pump to overheat and die. Manufacturers recommend that you NOT constantly operate the car below that level. The fuel is used as a coolant for the pump too. I've owned 12 Fords in the last 15 years, and rarely ever go below 1/4 tank, and have never had a failure of the fuel pump.
Test ohms resistance of the wires between pump and switch. High resistance, especially on the ground side (negative) can burn it out fast. A bad relay could be involved (corrosion increasing resistance) but this should show it up.
Make sure you're testing resistance of the inertia switch (usually in trunk) that cuts power to the fuel pump in an accident as well.
That's the simplified version. For further complication on the electrical side, see: http://www.allfordmustangs.com/foru...el-pump-diagnosis-101-1986-1993-mustangs.html
Also, try taking the fuel line loose and blowing through it. How freely can you blow through it?
And at the risk of offending, when was the fuel filter replaced last? Should be at least once a year.
Clogged fuel line or filter is like clogged arteries; hard on the pump. And for the same reason, the output pressure at the fuel pressure regulator should be about 40 PSI with the vacuum tube off it.
If all else seems good, consider a different brand of pump.