Security light on constant and battery drain

Hi the security light on my car stays on continuously even when the car is running and the battery will drain down over night if I don't disconnect it
The vehicle had this problem when I acquired it recently signed I had gotten a battery fully charged and it did all kinds of weird stuff from the gauges moving erratically and a clicking by the glove box which I found was coming from the bcm
So I replaced the bcm and Did the security relearn sequence of of this site and the car started but the light still stayed on constant from there on it started every time for about two weeks then one day the battery was completely dead si now I'm kind of wondering where to start looking? Possibly the ignition switch, a bad ground maybe I'm kind of at a stand still any thoughts or info would be greatly appreciated
Thank you very much really love your site has given me much information to do with all my vehicle s in one way or another.