Confirm there is +12 volts in and out of fuse F2.6 with the key in the start position. Use a KNOWN good ground for testing.
If there's no voltage there a problem in the ignition switch or wiring fault.
If there's voltage then check the clutch safety switch (CSS), starter relay, or starter solenoid.
To check the CSS switch test for +12 volts going into and out of the CSS switch with the key in start. It's also possible to test at the Starter relay pin #85. If no voltage, then suspect a bad CSS.
If voltage at starter relay pin #85 suspect a bad starter relay. You did swap didn't you?
1999-2004 MY fuse panel schedule:
http://www.allfordmustangs.com/foru...r-swap-wont-fire-please-help.html#post2669271
For a no crank problem this is not a bad fuel pump. A bad fuel pump will always have a crank with no start.