The oil pressure gauge on a Ranger is a switch. If you have 5 or 6 pounds of oil pressure (don't remember which) it will read normal. Less than that zero.
So is it the gauge in the instrument cluster, the sending unit or is it low oil pressure? Unless you can hear banging and clanging around in the engine you need to troubleshoot to determine which. If you do have banging and clanging, it is probably to late to just change the oil pump.
You can test it with a mechanical gauge to determine if you have oil pressure. Or troubleshoot the gauge and sending unit to see if it is working properly. I believe the sending unit just grounds the gauge wire when you get oil pressure. Pull the wire off the sending unit and ground it. The gauge should go to the normal oil pressure reading. IF not the gauge or wiring is bad.
If it does read normal, you now have two options, the pump is bad or the oil pressure sender/switch is bad. I guess you could have a bad oil filter; but, then you are back to the banging and clanging part. It is pretty cheap (compared to the labor to pull the engine/pan) to just change the sending unit. Oil pumps are pretty sturdy and rarely fail, they do; but, not often.