there should be a bress Y fitting at the back of the engine. one line goes to the pressure gauge the other to the filter, if no filter the line will go to the side of the the head to oil the rocker arms. Connect to the oil pressure side of the brass y fitting as this is a direct connection to the pump by way of a internal line. I would drop the pan and check the pump and lines from the pump . the pump has a brass bottom plate that could be worn on the inside. the pump gears should have a .001 clearance to this plate.If you wish to check this you will have to remove the pump[ two bolts] and Also check the spring to the pressure valve. I have also found the brass tube that takes the oil to the mains to have cracks in it. also have found the pickup screen pluged. Also check the gear that runs on the cam for wear. this is a few things that i have encountered. Herb in mi.