The oil warning lamp has several different indication:
Flashing or steady red plus three beeps: low oil pressure.
Steady amber: low oil level. Stop and refill. Opening bonnet resets the oil level trip.
Flashing amber + beeps: oil level indicator fault
Flashing amber means a
problem with the oil level sensor system. The sensor itself is the thing you've just plugged back in. There is also a microswitch in the bonnet catch, right at the front of the bonnet, which resets the oil level warning. Check this switch to see if it's OK.
This picture of my old Toledo with the bumper off shows the lock in all its mucky glory. The microswitch can just about be made out under the near end of the spring.
Obviously red means stop, stop the engine and find out why you've got low oil pressure. Continuing to run the engine will cause bearing failure. Steady yellow means top up the oil.