I have complete content at this website with images and simplified wiring diagram to help explain the funtion of the oil pressure switch.

Visit https://www.catalina36.org/forum/technical-discussion/36-mkii-oil-pressu...

The only circuit missing from the image below is that when the ignition switch is held at its most clockwise position, power is provided to the heat the cylinders by placing a temporaty short across the oil pressure switch. This also silences the buzzer.