This is a 2 terminal switch that is not closed (current flowing) until it senses pressure above 12 psi.
Install it somewhere in the oil pressure system and route the power for the ignition system (NOT start function) through this switch. When the oil pressure drops below 12 psi it will shut off the ignition.
This is also true for starting. As the starter motor turns over the motor it will not fire until the oil pressure reaches 12 psi (this usually only takes a few seconds). Optionally a user can install a momentary switch across the #43600 shutoff switch terminals (see Longacre #45460 or #45462). To start the motor before it reaches 12 psi simply activate this switch to bypass the shutoff switch.