Bob,
I have been improving my car for 19 years. I am an electronic and computer technitian and have learned a few tricks that I have applied to my car.
I wouldn't use the
oil pressure switch. Sometimes, it may difficult to start the car if the system is dry. You can make an arguement that there's always gas in the carb, but I have had problems with this. I do use an inertia switch from a Mustang instead. If you are in an accident, the fuel pump is cut off immediately, not after the pressure drops.
I wired a relay (located in the engine compartment) to the ignition switch. The relay takes the current load off the switch and powers the fuel pump and MSD ignition. This relay is also wired through the alarm system so that the car can only be started after the alarm is disabled. The Clifford alarm system also pops either door open. This is very useful if the top is on the car.
A second relay from the ignition switch powers up all the circuits that I want to activate only when the car is running: wipers, radar detector, back up lights, heaters, radiator fan and etc.
You really want to set up a master power off (kill) switch in the big wire from the battery to the chassis ground. You could put this in a hidden location, but they are large and it's not easy.
I'll see if I can find a diagram for you.
Paul