Ford uses the Ground on the fuel pump relay for the trigger.
The computer controls this ground.
One side of the relay's coil gets 12volts from the EEC relay when key is turned on.
But the other side of the coil, the ground, connects to the computer, computer will ground the relay for only 2 seconds when powered on, then it won't ground it again until engine RPMs are above 500, engine started.
This is secondary safety feature so if engine stops running(falls below 500rpms) from a major malfunction, or accident, the fuel pump power will be cut off.
Inertia switch would be the Primary safety feature.
Fuel pumps power path
Battery------fuel pump fuse-------fuel pump relay-------inertia switch----------fuel pump-------ground
Fuel pump relay's power path
Battery----key------EEC relay-----fuel pump relay------computer-----ground
With key off you should find one 12v contact in the fuel pump relay's socket, that's from the fuel pump fuse, it is live 24/7
With key on there should be one more 12v contact, that's the relay's 12v power from the EEC relay.
EEC relay gives power to computer, fuel injectors and most sensors, also the fuel pump relay, when key is on.