Congrats on finding your Ericson. Welcome to the forum.
As you will soon discover, finding "ORIGINAL SCHEMATICS" while it seems like a needed item is most of the time of little value on a boat of 40 years. Previous Owners have likely altered most if not all of the systems.
We buyers of "Mature boats" have to make our own schematic. This usually means crawling through the boat and looking in all voids and compartments to discover what is inside.