I recently bought a Clark C500 Y50 Model, 5000 lb pneumatic tire model with a Waukesha gas engine. When i bought it The oil pressure and temperature gauges were not working but it ran fine. I just finished repairing the entire wiring harness but the oil pressure gauge was still not working. I replaced it with a mechanical gauge with a 1/8" tube from the sensor location to the gauge. Still no oil pressure. This engine has the bypass oil filter system with a short line running to the filter from a tee on the side of the block where the oil pressure sensor is located. It also has a long hose running from the filter to the opposite side of the block. I disconnected the short hose from the block to the filter and ran the engine - I only get a real small dribble of oil from the hose - it took 30 seconds to fill half a cup with oil. Seems like there is no oil pressure at this location where the oil pressure sensor and filter are connected to the block but the the engine the engine runs smoothly at all rpms with none of the noises I would expect to hear from rod bearings or rocker arms with no oil pressure. Is it possible there is a blockage in the oil flow to this location but the rest of the engine is getting oil pressure ?

My problem is how to figure out if the low oil pressure is because of worn out engine bearings or an oil pump failure or something else like a blockage in the oil gallery to the pressure sensor location but I am not sure how to do that.

Appreciate if anyone could give me some pointers on trying to figure out what the problem is -is there any other location I can test for oil pressure or flow from the oil pump ?