help! wierd oil light problem

Those senders vary but should turn the lamp off at about 9 p.s.i.Through testing with a gauge you'll likely find 25 p.s.i. or better at cold start.Oil pressure drops as engine gets hotter. Typical condition for well worn engines.You don't need to overhaul it today but you can. If you wait until it pokes a connecting rod through the side of the block ( typical for well worn slants ).... Good luck with it.