locating the PRV on an escort mk5 RS 2000

[slideways]

Hi all
I am trying to track down the cause of my oil pressure light glowing faintly and intermittently, I have change the pressure switch and the light is still there,
With engine off, Ignition on the light is fully lit as you would expect,
engine running light glowing faintly but sometimes it will not be on at all irrelevant of oil temperature,

I have read that the prv /oil pump has a bolt that comes loose and causes a drop in oil pressure,How do i find this bolt to check if it is tight?
Failing this I thought it might be a dodgy earth any clues to the relevant earth point?

Cheers
Slideways