I would suggest that you start at the basics, check and clean ALL the earths as you could have some circuit back feeding due to a bad earth. Put a small 12V bulb in line between the positive terminal of the battery and the battery terminal that you have removed make sure it does not touch anything and short this will light up if there is a current draw. If the bulb is lit start disconnecting and reconnecting systems until one switches of the light bulb when this happens you have found the current drain.