Another option would be to use an ice pick type 12 volt test light, and connect it in series with the battery cable. If there's enough current draw to make the light burn, or even glow more than dimly, you've got enough parasitic drain to draw the battery down. One common cause of an overnight battery discharge is the rectifier in the alternator. Try disconnecting the big charging wire from the alternator and see if the overnight draw-down stops. Don't let the exposed ring terminal touch anything- - - -it's best to insulate it with tape.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!