How can I check the oil pressure switch? The bit that actually screws into the engine block? Without the engine running should the terminal on it be connected to ground (ie engine bock)?

Cheers

G

if you measure the resistance between the out case and the spade terminal, when its out of the engine, or with the engine not running, you should measure 0 Ohms, or near that. This acts as a 0v switch, and in this state the oil light would be ON. As pressure builds up, the switch goes open circuit and the 0v feed is lost, hence the oil light will go OFF.
Hope this helps

These days two types of oil pressure switch exist "normally on" and the more conventional "normally off".

Normal (non competition) style switches switch anywhere between 3 and 10 psi.

To test to as Berwyn suggests it should either go from "on to off" or "off to on"

use a match stick to press on the diaphragm inside the switch,check if continuity comes n goes

Earth the wire from the light direct to the block to check that the light, wiring etc are all ok. Earthng this wire should bring the light on.