The oil pressure sensor on a Cummins engine is located behind the ECM harness on the driver's side. To get to it, remove the fuel filter housing and loosen the Allen bolt from the ECM harness.
Replacing the oil pressure sensor will solve the problem of a gauge not correctly measuring the oil pressure within the engine. Oil pressure sensors range in price, depending on the engine size.
Replace the oil pressure sensor by disconnecting the battery and removing the fuel filter housing. After loosening the ECM harness, remove the oil pressure sensor by taking out the bolts holding it in place. Install the new sensor and torque the bolts to 18 ft.-lbs. of pressure.