1997 Ford Explorer Oil pressure gauge & check gauge lig

The problem started with the oil pressure gauge indicator jumping when the brakes were applied. Additionally the check gauge light came on at the same time the gauge jumped. Now it seems that the oil pressure gauge is pegged out, looks like it has gone all the way counter clockwise to below the L. The needle sits directly below the pin near the L when engine running. When the engine is off the pin drops even lower below the pin. Checked oil level and seems ok. Not sure if this is an oil pressure sending unit issue or something else. Any input would be useful.