The system will work just fine with or wihtout the FPSS installed. The wires that would normally go from solenoids to FPSS should be grounded to the chassis if not using the FPSS.
I ran my systems without the FPSS.
What does it do? It cuts off nitrous flow if it detects a drop ni fuel pressure, which happens when you miss a shift, if the fuel pump fails, if the fuel filter is blocked off, if your injectors get clogged, or if you over-rev and hit the fuel cut, etc.
It is a good fail-safe system to have, but I didn't feel like tee-ing the fuel line - plus, I only missed one shift in 6 months of racing on the gas.
Chances of your motor being ruined by nitrous are (in my opinion):
40% bad install
40% leaky/malfunctioning nitrous solenoid
15% hit fuel cut while spraying
5% missed shift, hit fuel cut while over-revving.
Basic rules: check your solenoids/connections/fittings/bottle regularly, shift BEFORE redline, don't speed-shift while on nitrous unless you are really good and have good synchros.
93 Probe GT - for sale! $5,300.
95 Probe GT - the 007 version - smooth and refined.