I would start by purchasing a new oil pressure warning light sender.
Make sure the crankcase is full.
If there is no change, the next step is to install an oil pressure gauge and check the real pressure.
I did a short thread on this about a year ago.
Uncle "Richard" Douglas has a Land Rover with big wheels that never gets stuck... until he breaks something so it won't go. Uncle Douglas always breaks something. - Anna Crowther at the Conclave 2012 (AKA Carburetor Neck)