It's simples get a gauge with a sender, on top of the oil filter housing there are blanking plugs take one out and fit the sender, the wiring may be specific to the gauge but normally it's a live a nrg and an ignition feed.
Ta Phil on my Diesel there are only two plugs on the oil filter housing....one for the high rev/low pressure switch and one for the turbo oil feed pipe.. so where would I fit the sender??
I thought there were three on the oil filter heads you could get rid of one if you wanted and use an after Market as long as you know what pressures they run at??
Or if you get the cheaper sender that only does the oil presure and you still need an outlet for the presure switch you will need one of these to give you two holes.