My Spitfire's oil pressure switch.

The 3 prong oil pressure switch on my 79 spitfire operates the anti run on valve and turns on the low/no oil pressure dash light. If you remove the ARV the 3 prong switch can be changed to a single action, grounding pressure sensing switch to turn on the dash oil light. I have changed 3 of these switches on my spitfire. This switch failed because the gasket was folded, and didn't hold the 80 pounds of oil pressure from the engine. The video shows oil seeping from the plastic holes the prongs poke through, checking the contact's operations, pressure switching operation, and dis-assembly to have an internal look at what is happening as pressure moves the contact (washer) from "S" to "I" (how it works). "P" is the common, it's connected to the electrical harness, grounded to the frame. The switch does not supply a hot lead, rather it supplies the grounding half of the circuit for the oil light, and the ARV.