I had an erratic oil pressure gauge on a truck I bought in Michigan and drove home. 5 minutes from home, after a 4 hour drive, the oil pressure gauge started going crazy. It finally dropped to 0. I replaced the pressure switch and still had no pressure. I'm glad I shut it off instead of driving the last 2 miles.
Either buy a mechanical gauge, or buy a new pressure switch. The switch is cheaper but the gauge will hopefully eliminate any electrical issues that might be wrong with the gauge on the dash. If it doesnt show a pressure, then I'd say its your pump.
97 F250 7.3L CCSB
08 F350 6.4L CCLB
06 Ranger FX4 Lvl 2