If it is a drain, they can be elusive. I have had two that were intermittent. The one I discovered when I went out to the garage and the interior lights were on. Turned out it was a rusted connection from the door handle that turns the lights on when you push the button to open the door. Disconnecting took care of it. The other was the electronic level control module would energize by itself and drain the battery. Spent a lot of time on the floor testing circuits with no luck and then all of a sudden the test light went bright. $300 part so just pulled the fuse.