Originally Posted by SouthArk370Z

The wire from the NO relay contact goes to the white wire of the NMU to tell it you are in the desired RPM band.
The micro-switch says you are at WOT and enables the system.
The fuel pressure switch shuts off the nitrous if you lose fuel pressure.

So, as long as main power switch is on, fuel pressure is high enough, gas pedal is on the floor, and RPM are in the target band, you will spray nitrous. If any of those conditions are not met, nitrous shuts off.

Without a main power switch, you may not be able to cut nitrous if the WOT switch fails closed.
Without a fuel pressure switch, you can continue spraying nitrous when the A/F is lean.
Without a WOT switch, you will spray nitrous whenever RPM are in target range.