My Security light comes on (dash light) if the car is turned off keys out.

What is your question?

If I leave the van (actually an RV) off the security light will come on and stay on and drain the battery. I bought this vehicle used and it has had some modifications done by the coach builder at the factory and then by the previous owner. It has a keyless entry that appears to be aftermarket and I can not find it to disconnect. It has a trailer brake system and an aftermarket radio. The dome light did not come on when the door was opened and recently I disconnected the battery and after reconnecting it the light works again. The car shows no diagnostic codes and runs great. If I put the key in and advance to run position it gets rid of the security light. Could it be a bad bcm causing this?