Mystery bulb socket behind dash

Craig; There is an oil pressure light located on the far left upper part of the instrument panel. It is separate from the circuit board area. Put a bulb in the socket itself. With the engine off, and the ign. key in the run position, the light should be on. If so, pull the wire off the oil sending unit. The light should go off. I found it difficult to install. Big old hands don't help.