OK, what's the deal on oil pressure switches. I know they fail often, but -

I have just replaced both on my 2.8 (1993) 12V, 0.25Bar and 2.5Bar. Now I get a warning light and chime at 1500 rpm, which goes out above 2200 rpm.

The car has done 140000 miles, so I guess some bottom end wear is to be expected, and thus a drop in oil pressure.

Are there any alternative switches I can fit, say 1.5Bar etc ?

I don't have an oil pressure gauge, so I can't tell what's really happening in there.

Did you plug the correct wire on the pressure sender?

There are two wires, and if you plug the wrong one on, it will give you a warning light.

As a guide, below 2000rpm the oil pressure is governed by the 0.2bar switch and above 2000rpm it is governed by the 2.5bar switch. So if the engine revs are below 2000rpm the oil alarm will sound if you have less than 0.2 bar. Above 2000rpm the alarm will sound if you have less than 2.5bar.

Before you changed your pressure switches did you have a problem with the oil warning? Hopefully you have the sensor wires on the wrong sensors or the sensors in the wrong positions. At worst you may have an air pocket forming in the pump but this only happens on cold starts.