The "Oil Warning Light" is a low oil pressure warning, not an oil level warning. The Oil Pressure Switch is located on the lower left front side of the engine and it screws into the oil filter adapter.
Pressure can be affected by a low oil level, of course, but it also could be a defective switch. I wouldn't think a new switch would be too expensive to replace and it ought to be a fairly easy job. I'm assuming you have made absolutely certain that the crankcase is full.
C.B.