2005 ponitac air bag issue

Hi there, My air bag light came on about 2 years ago and the car is not on the list of a problem. It's a 2005 Bonnie with 78k on it, other than that the car is fine. The bag came on after a night of being parked during heavy rain. Could it be a relay under the hood or the back seat/ If so which one they are not labeled for the bag. Thanks