3007 Aft Cabin Engine power circuit query

[PCOMT]

I have a 1981 3007 aft cabin. I have reviewing and drawing out the starting power circuit because I am confused by the 3 batteries and how the house circuit seems to be designed.

I drew this schematic/design based on the wires I followed.
What led to this initiative was the fact I could start the engines no matter which position the switch was in. If it is in position 1, I start from the battery #3. If it is in position 2, I pull from the battery bank consisting of battery #1, Battery #2.

I want to add a larger battery bank and install an inverter, but I need to understand the existing system to ensure I can rewire the engine batteries to work with the engines only. The new bank will become the house bank and power everything except the engines.

My questions are:

1- How does the alternator output tie into the existing circuit? ( I forgot to follow the wire when at the boat the last time)

If this was a domestic car, I would expect the alternator output would tie into the starting circuit and feed back to the battery on the main line. (I could be on the wrong return wire)

2- Does anyone know if this is the case?

3- Can / Should I wire the engine batteries directly to the engines, bypassing the battery selector switch and depend on the ignition circuit to isolate the power from the system?

4- Does anyone have a diagram that would be better than what is installed now?


Note:

The charger has 3 outputs, not 3 chargers

[PCOMT]

This is my proposed *new* circuit.

Intent:
Ensure all battery banks can be charged while either engine is running
Ensure all banks will be charged when on shore power
Ensure electronics do not experience low voltage trip when main circuit is loaded up (starting engines)
Ensure inverter / house loads separate
Ensure to always have an emergency battery for fool proof starting

Operation:
Normal usage will be to run Bank # 1 (90%)
Occasionally run bank # 2 to exercise the battery (10%)

Notes / Considerations:
Battery separator will allow alternator to charge bank 3 once the main batteries are at full voltage, protecting the starting batteries
120 VAC charger will charge all 3 banks when plugged in to shore power
Diode will prevent bank 4 (electronics battery) to flow to bank 3, preventing low voltage to electronics
Bank 1 & 2 should be regular engine start batteries
Bank 3 & 4 should be deep cycle batteries
Electronics battery can be a smaller size (less load)
Additional batteries can be added to any banks as required
Separator is different than a battery/charging isolator used in RV installations

Any thoughts / Ideas / Feedback?

[AaHubb]

First issue I see is sorting out which battery controls the ignition switches and dash gauges.

[PCOMT]

Currently, the power comes from which ever bank is selected. 1,2 or both.

Most gauges are powered by the port engine ignition switches.