1smoknjoe, sounds like you may have either a bad sensor, or a wiring problem, with the key on and the engine off, obviously there should be no oil pressure to read.
I would recommend disconnecting the sender wire from the sender and powering the guage back up, then short the sender wire to ground and see if it sweeps to "past max", the sender has to be matched to the guage, they sort of look like a small can with a rounded top with the wire terminal on the very top...its a bellows type sender that moves inside against a reed type carbon pile.
Got a pick of what you have? Did the sender come with the guage? It's ok to mix and match, but the sender has to be the right range as far as resistance value (Ohms). Stewart Warner I would have to say is the most common of years past, but a lot of the auto parts stores now carry less superior guages which have odd senders and won't work with the older stuff.
By "Grounding the sender" I simply meant the sending units metallic body must be grounded through the threads to work, some people before have used say Permatex #2 on the threads and they won't conduct enough to work right, a little teflon tape and anti sieze are all I use on mine, they don't leak and they work, although sometimes the oil leaches out of the anti sieze and looks like a leak, just clean it off a few times and they're fine.
GT
GT