Pull the wire, clean the contact surfaces, consume a martini for the water gods of vagary and try again. It may not help but you will feel better for having done it, it may require a second martini. It also may indicate you should run above 1600. Good news is that pressure is indicated.
sending unit or bad ground .
Both are possibles. Usually a loose wire on the sending unit causes this.
Had this problem before. Stuck oil filter by-pass valve causing the oil pump relieve to cycle. CHANGE YOUR OIL FILTER.