It is my belief that the switch runs on an earth return to the bulb. So yes, the bulb must have a live, ignition derived feed to one side of it`s holder and the oil pressure switch makes the earth.
With oil pressure within the correct range the switch is in effect open circuit, if pressure drops off the circuit is made, lighting the bulb.
The light should be illuminated when the ignition is turned on, it should then go off when you start the engine (with oil pressure) and only illuminate if oil pressure drops below the switches threshold when the bike is running.
Have you earthed the opposite side of the bulb holder? Maybe if you utilise the position within the idiot light array there is a common earth rail already there, perhaps that requires to be isolated to that particular bulb holder?
Quote from your post:
I have checked the continuity through the Oil pressure switch circuit to earth and have continuity whether the engine is running or not so is it the switch is U/S or have i wired it up incorrectly
I also have Eisi`s switch but am yet to fit it and I don`t have it to hand.
If there is only one terminal you must check continuity between the terminal and switch body, if there are two terminals you need to check between them both with your multimeter.
WITHOUT pressure you should indeed have continuity.
