Ayuh,.... Donno what ya bought, But,.....
An oil pressure sender tells the gauge what to show,....
Ya need an oil pressure Switch, to wire the fuel pump through, so the fuel pump can't/ won't run unless the motor is Runnin',.....
To power the fuel pump, only when crankin' the motor on the starter, run another wire from the outside tiny terminal on the starter's solenoid, directly to the fuel pump,....
Once the motor starts, the ignition power through the oil pressure switch will take over,...