No really good way. What I'd suggest is eliminate as many as you can first (like the battery interconnect wires) by tracing visually where they go.
Then disconnect the others one by one and see what stops working. i.e. if house lights stop you've found the house 12V feed, if chassis lights stop you've found the one going to the chassis-related stuff, same for jacks working and generator starting, etc. Just make sure to insulate the ones you disconnect so you don't have any problems
.
Stewart