A competitor recently asked me a question about the safety of electric fuel pumps in race cars. The problem was the cars that originally had a mechanical fuel pump, the new electric pump would run until the fuel pump switch or master switch was turned off. This could be a problem in an accident if the motor is not running, (most people could easily forget to turn off the pump). This is also a problem on cars that originally came with electric pumps and the emission control computer has been removed. This problem is easily corrected. A low pressure (under 10psi) "normally open" oil pressure switch can be added to the fuel pump circuit to activate a relay which controls the pump. With the engine not running, there is no oil pressure, and the pump doesn't run. To install this system, the original oil pressure sending unit can be removed and replaced with a "T" adapter. The sending unit is screwed into one port on the "T", with an oil pressure switch in the other port. Check with your local auto parts store for a switch to fit your size port. Echlin makes Normally Open switches with 2 terminals in most thread sizes. To wire the system, run a wire from one terminal of the switch to the coil of a 12V relay. The other terminal of the switch gets connected to ground. The other side of the relay coil is connected to a +12 circuit AFTER the master switch, and after the "ON" position of the ignition switch or a separate fuel pump switch. This terminal of the relay is also connected to the Common contact of the relay. The Normally Open contact of the relay is connected to the + lead of the fuel pump, and the - of the pump to ground. Now if the car is running, the oil pressure switch is closed, which energizes the relay and this closes the Normally Open relay contacts turning on the pump. If the engine stops, the oil pressure drops and opens the switch, which de-energizes the relay, opening the contacts and turning off the pump. When the master switch or fuel pump switch is turned off, the entire circuit will loose all power and the pump will stop.
 

If you have trouble finding the N.O. switches with a thread for your car, a N.C. oil pressure switch will work. These only have one terminal (the other contact of the switch is the body and will be grounded). With this, you will use the N.C. contact of the relay instead of the N.O. Make sure that the wire to the oil pressure switch is secure and run in a way that it will not be inadvertently removed, or the pump will run with the engine off if the main power is on, but will still shut off with the main power or fuel pump switch since the pump and relay are connected after these switches.