You have a circuit that keeps draining the battery (power draw).
You will need a digital voltmeter, a notepad and a pen to start with. You need to start with a fully-charged battery (not charged by the alternator, but an external battery charger). Record battery voltage prior to installing the battery in the vehicle. Install battery terminals. Record voltage. There should be some drop in voltage.
Now remove one fuse at a time and check the voltage, and then put the fuse back in. You need to keep a good record on which fuse and voltage increase (if any), and what the fuse controls.
Once finished, whichever fuse that you see a voltage increase is where you want to concentrate in looking for the power draw.