1988 mercury grand marquis oil light came on. on 1990 Mercury Grand Marquis

What could make an oil light come on when oil level is reading good

Asked by for the 1990 Mercury Grand Marquis
The oil pressure warning light is designed to come on when oil pressure dips below 3 to 7 psi. At that stage damage is being done to the engine so if it has been on for a while it is most likely a defective oil pressure switch which is probably less than $15 in parts and take a half hour to fit.