What I learned from ruffram's truck - The ECU should power up the main relay when you turn key to run position. That puts power on all the sensors. You'll see 12 volts come on to some of the fuses. Then, when you turn key to crank, the Body Control module tells crank relay to pull in, and the ECU must check for engine actually turning from crank posituion sensor. If ECU is happy that engine is actually turning, it supplies spark and fuel relay is pulled in.

So, since you have cranking, you are not immobilized and body control unit is working.

If you can read 12 volts at fuse 2 in underhood box, main relay is energized.

Inertia switch controls main relay, so if 12 volts at fuse 2, main relay is "ON" and inertia must be OK.

That leaves the fuel pump relay to be pulled in by the ECU applying a ground, and it must need sensors to tell it to do that, and Crank sensor is first on the list. There are also fuses to the iginition coils, that's #24 and #10 in the passenger fuse box, along with ignition relay.