The ZD30 Motor has 2 oil pressure switches a 15psi one (on the passenger side) and a 25psi one (on the drivers side)

It is not Un-Common for them to give trouble and cause the oil warning light to come on

On the common rail motor they are different form one side to the other, and cannot be interchanged.

Warning: if your oil warning light comes on, DO NOT assume there is a fault with your switch, and have the oil pressure checked properly before driving the car.