1999 Cherokee Classic Oil Pressure Gauge Started Showing High Pressure But No Check Light And Still Runs Good

Car has under 100,000 miles and has been well maintained with the oil being changed every 3,000 miles. This problem started suddenly on one cold morning (the car is not garaged). Instead of peaking at the normal gauge position near the center, the pressure started as it usually does, but continued to climb and maxed-out on the gauge. No check engine light or other indications. After allowing the engine to cool and checking the oil level, restarted with the same indications — pressure built as it should, then maxed-out on the gauge. Suspect either a faulty sensor or gauge. How do I check the sensor with a voltmeter and where is the sensor located?