I use an oil pressure switch, but also added two bypass switches. One to prime the system, the other to disable it for anti-theft. I also have a nitrous type trigger switch on my outboard carbs to kick the pump up to high speed when they are opened. I run a Fuel Labs 2 speed pump.

Of course the switches including the oil pressure switch only interrupt the low amp side of the relays, or the trigger voltage. I use 2 40 amp Bosch relays to feed the fuel pump.