oil pressure switch dashboard indicator

If the oil pressure light does not come on when key on, engine not running then you have either a bad light bulb, a bad oil pressure sending unit (sensor which grounds the oil pressure light circuit when oil pressure fails), or a wire has become disconnected. The easiest troubleshooting method is to find the sending unit, disconnect and ground the wire and see if the oil pressure light comes on (assuming, of course, that the key is on and engine not running), if the light comes on while grounding the wire, but not when wire is connected to sender, replace sender then confirm light works correctly and turns off when the engine is started. If you find the sender, but no wire is attached, look around in the general area for a loose wire with the correct type of connector on it.

If grounding the sender wire does not turn on the light, verify that you haven't blown the fuse for the instrument panel, and then replace the light bulb.