Vw polo 1.4 1999 oil light comes on at 3000 revs

Had exactly the same problem, completely baffled us until we discovered that the it was the oil pressure switch. We had already replaced it with a new one and then that didnt fix it so we fitted a new oil pump, but as soon as it was revved over 3000 revs the oil light came on. It turns out that there is actually a choice of 2 oil pressure switches for this car (1999 1.4 polo) one works only low pressure (black cap) and is the wrong one, the other works on a higher racio (green cap) its the high pressure one you need. If the oil light was on at tick over or below 3000 revs then its the lower oil pressure switch needed, above 3000 its the higher one. The parts people insisted there was only one, but there is definately a choice of 2 and it fixed ours instantly.
If it was an older model they actually have 2 switches on the car itself and one is a high pressure and one is a low pressure (just incase anyone needed to know)