Cpt.Zanzibar

ok so i busted out the good ol volt meter, placed the 2 leads on the post and one on the cable. i got a reading of 12.34 volts. so i start removing fuses and nothing. i move to the engine bay and remove those fuses, well when i remove the BTN 60A fuse, the volts rapidly drop. could this be the culprit of my battery drain? where do i go from here? Ive been looking at wiring diagrams but i cant seem to figure out what the BTN circuit is or what it does. all help is welcome!