But, now that you have hopefully simulated the micro switch working, as far as the car knows, and if the oil was high enough, and of course if the bonnet switch is faulty, you should now have cleared that oil level warning. If it is still there, the root cause lies elsewhere like the wiring, maybe a fuse, or the oil level sensor.

I’m guessing that while the bonnet switch lead was unplugged that the car would think that the bonnet was open, applying a short should, I’m guessing look like the bonnet was closed.