Wiring diagrams are basically like road maps. Assuming everything works accurately that fuse 19 powers, you might need to back-trace from the fuse. From looking at the 3rd diagram, fuse 19 receives power from "Relay-auxiliary circuits" on connector C0581-3. I would repeat your battery drain test, now knowing when fuse 19 is pulled, your drain goes away. This time, instead of pulling the fuse, pull the relay that feeds the fuse and see if the results are the same. There is a chance the relay is stuck in the "closed" position and is always feeding power to that fuse.

 

pulled the relay-auxiliary and the drain was still present