[edwardc]

An additional point to ponder. In the original "conventional" wiring diagram, a heavy #4 (or larger) cable runs from the battery switch output to the the main terminal on the solenoid. ALL other DC loads are then taken from solenoid's large terminal.

To me, this doesn't make sense. When starting, the large starter motor current (around 60A?) will cause a noticeable voltage drop across the length of #4 wire. You can easily measure this by putting a voltmeter on the solenoid bat terminal when cranking. Often, the #4 wire size is undersized, given the total length of the "back and forth" wiring runs, and the voltage drop upon cranking is enough to "crash" sensitive electronics, even though the starter couldn't care less about it.

Instead, why not have a positive DC bus bar located close to the battery switch. The #4 starter cable, and ALL other DC loads, can come off of here. This avoids propagating the large-ish voltage drop of the starter circuit into all of the boat's electronics.

On my boat, with the original "conventional" wiring, the autopilot crashes and resets to "standby" mode when the engine is started, and the AIS portion of the radio hangs and simply stops producing position reports. Both of these conditions are easy to initially overlook until you realize that "something's not right!..."

In my upcoming DC rewiring/Lithium Battery upgrade, I plan to go even one step further, using a dedicated start battery that will completely isolate the starting transients from the DC house bus.