Back in the day a friend of mine had a very old Mini-Cooper ( a proper one, not the ones that BMW call minis now and which are the size of a Land Rover). He had trouble with the oil pressure warning light coming on frequently. When I next saw him I asked him how the problem was going.
"No problem. Fixed it in a jiffy."
"What was it?" says I, "Oil pump, oil filter blocked?"
"Dunno" he said, "I just took the bulb out!"
So there's your answer. :-)