It might be useful to draw a crude diagram of everything: battery, switches, starter, ebox contents... everywhere there’s a connection relevant to your problem. Then label each connection with what you’d expect to measure at that point compared to a reference point (under whatever conditions are possible... something like “start switch depressed”). Then just go around and verify all of those. If you get everything done and measured matches expected, you maybe measured wrong, expected wrong, or missed something else. If measured does not match expected, that would be valuable info and likely narrows things down a lot. Perhaps even pinpoints where you have a problem.
Either way, it’d organize your debug instead of being scattered across a series of posts. Aka: Condense the info.