The only right way to check this out is to measure the oil pressure directly... this isn't something you can guess at.

The only thing short of that is to make *absolutely* sure it's not an electrical fault. Pull the wire off the pressure switch, and measure the voltage between it and ground with the engine idling. A good ol' analog meter (or test light) is more useful here than a fancy DMM because you're looking for a brief interruption in the voltage, which the DMM might not 'see' due to its display refresh rate. At any rate, what you want to do is to satisfy yourself that the 12v supply to the pressure switch is not being interrupted due to deteriorated wires or connections which get flexed as the engine moves in its mounts.

If your 12v to the p-switch is solid, then you really do need to measure the oil pressure directly. You can probably cobble up something temporary between the switch port on the block and a cheapie mechanical pressure gauge (80-100 psig range). The nuisance is getting the right adaptor for the metric thread on the block and the "english" fittings on the gauge. Or... go whole hog and install a permanent oil pressure gauge. The electrical ones are conceptually simpler, but I prefer mechanical and went that route.

When I finally installed the OP gauge last year I was quite pleasantly surprised to see some solid readings - 30-40 psig at idle, and 60-65 on the road. This is on a '92 with 245K on it that I've flogged pretty hard over the past 100K. My hunch (and hope)is that you have an electrical problem.