RE: 94 F150 Oil pressure gauge problem
1990 150k mine does the same thing, its probably the gauge not the oil or you would have all kinds of trouble the lifters hammering away dry just for beginners. check the wire from the sensor to see if it might be rubbed off and bouncing arround grounding out, even just a small rub will cause all kinds of headache. otherwise it will probably end up like mine I just hope the idiot light works if I do have a problem.
if you get pressure when you rev the engine it could be a problem like old oil or worn pump.
my fuel gauge did the same thing about 3 months after the oil and now I think the temp gauge is staying right in the middle, I need to check it next time I drive it. by your description you probably have the same issue I do. I priced the gauges at 400.00 from the dealership as a package with a core. not worth it to me. just pour in the 100.00 gas every monday and hope it blows up before next week so my wife will let me get a new one.
probably not a great help but for what its worth.