OK so you have a Class "A" Motorhome with a 7.5L (460) EFI on a Ford F53 Chassis with one high pressure fuel pump in the tank.
The 1.2 v is coming from the Computer pin #8 over the Brown wire that checks the fuel pump relay and fuel pump status. The Brown wire also carries the current from the fuel pump relay NO contact to the input of the Inertia fuel shut-off switch.
The fuel pump relay is closed when the Computer pin #22 (Tan wire with a light Green stripe) grounds the coil of the relay. This wire also goes to the EEC self-test pin #6 and can be grounded or shorted to pin #2 of the self-test plug to run the fuel pump for testing. The computer will ground the fuel pump relay for one second when the key is first turned on and again for one second every time it sees a PIP pulse. The fuel pump runs at no other time pressure or no pressure.
The common contact of the fuel pump relay is fed from a fuse link by the starter relay over a yellow wire. There is a fuse link at the starter relay that will cut power to the fuel pump wiring and the yellow wire going to the fuel pump relay Common contact.
Power to the fuel pump relay coil is fed from the NO contact of the EEC Power Relay over a Red wire.
The fuel pressure regulator just bypasses fuel back to the tank when the fuel pressure goes over what the spring and vacuum says it should be. With the engine not running the regulator will by pass fuel to maintain 40-45psi with pin #6 of the EEC self-test plug grounded or shorted to pin #2 of the EEC self-test plug with the key on.
With the engine at idle and at max vacuum the fuel pressure will be about 30-34psi.
The HP frame fuel pump will pump to about 95-100psi into a closed head and will run all the time it has power on it. But the fuel pressure has nothing to do with the running of the fuel pump.
A PIP pulse comes faster than a second from the distributor when the engine is cranking or running so the pump will run all the time the engine is cranking or running and has nothing to do with pressure. When the engine is not cranking or running their is not a PIP train so the pumps will not run with the key just on.
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