i would like an answer or at lest tell me you can't answer
thank you for replying just extra info timing belt was changed at same time as water pump
the header tank cap is also constantly hissing.
Could a new pump have failed?
is there any bleed points on connect? i haven't see any
both small return pipes when revving engine have return flow.
I'd 1st suggest measuring the actual oil pressure with seperate mechanical gauge - this can be plumbed into the engine via the current pressure switch port - if you use a Tee piece you can keep the pressure switch plumbed in as well and so see if the low pressure light corresponds to a low pressure reading.
As its intermittant and you have no rumbling or rattling noises from the engine its likely to be an electrical fault so 1st check the connection to the pressure switch is bright and clean and check back along the switch wiring for any signs of damage to the insulation
As if the wire is grounded out at any point then this will also turn on the light.
If you do have a low pressure reading and to turn on the light it will be very low about 5psi then replace the oil pump and ensure that the pump pickup in the sump hasn't come loose or is blocked