If it's a parasitic drain the method used in automotive is to disconnect your live battery terminal put your multimeter in line switched to amp's, then pull each fuse one at a time until you see the meter move down, that will give you the starting place to look into each piece of equipment attached to it.
Remember you may have equipment attached into the wiring so unknown untill you investigate. A lot of modern equipment does consume power even when switched off, like car radios, gps, and equipment on standby.
I think there is a video on Utube, have a serch for it.
Hope this helps.
Odysseus
Bav 38