[Alex W]

The best thing is to trace all wires from the battery and battery switch and draw a picture of how they are connected and what they are connected to. That will make it easier to understand.

Do you have an electrical meter? It sounds like your 1/2/all switch could be failing. A meter testing for connectivity would be able to debug this.

My electric start outboard also has a pullcord. It was a Tohatsu/Nissan.

 

[Alex W]

Without labels on where the wires go it is very difficult to see what is going on there. For instance I can't tell if the batteries are wired in parallel, or if each battery is wired to the switch. If it is the latter then why are there two high current wires on the left battery, and where does the second one go?