Oil pressure sensor ........ updated

ok so I got a new oil pressure sensor (goes in the side of the head) in an attempt to stop the buzzer going off, took the old sensor out confirmed the part numbers match, stuck the new one in………and now the oil light doesn't stop flashing??? stuck the old one back in the light goes out, whats that all about? do the new sensors need to 'bed in'? so I'm back to where I started!
Any ideas? Thanks