Originally Posted by Just Dave

Go to NAPA and ask them for the Echlin book, and look for oil pressure switches (they should be OPXXXX part numbers). Look through the description and you'll see the thread size, psi rating for the switch and also whether they are normally open or closed. You want a normally open. This means that with no outside action, the circuit is open. If pressure is reached, it closes the circuit and turns your pump and fan on.