on the 93 at least the inertia switch get its power from the EEC relay, and then that feeds the fuel pump.
https://sites.google.com/site/sn95mustangs/tech-info/94-95-ccrm
Some EEC relay diagnostics: If it seems like none of the EEC systems are receiving power (underhood solenoids, fuel injectors, etc), here’s a place to look. First check the PCM/CCRM fuse in the underhood fuse box (20 amps). Also check the ignition switch fuses.
At the CCRM (Constant Control Relay Module – the black box mounted on the radiator overflow bracket): With the key turned to run, check Pin 12 and 24 for accessory power. If it’s there, the issue lies past the CCRM. If there’s no power: Check CCRM Pins 8 and 10 for constant 12 volts. Check CCRM Pin 13 for accessory 12 volts. Check CCRM Pin 15 for ground. If 8, 10, 13 and 15 are present (this requires the key to be on), but 12 and 24 are not showing 12 volts, that suggests a bad EEC relay inside the CCRM.
Fuel pump relay diagnostics:First, always check the inertia switch in the trunk and the fuel pump fuse in the underhood fuse box (20 amps). Also check the ignition switch fuses. With the key turned to run and checking within the fuel pump prime-out period (a duration of 2-5 seconds after turning the key to run): Check CCRM pin 5 for accessory 12 volts. If you have it, the issue lies downstream. If not: Check CCRM Pin 11 for constant 12 volts. Check CCRM Pin 13 for accessory 12 volts. Check CCRM Pin 18 for a ground signal during the prime-out.
If this is all good, check the inertia switch (located in the driver side trunk, adjacent the tail light) and fuel pump electrical connector at the tank.