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