battery system overview - 2003 24v Limited

[toastie22]

I have an '03 24v with dual battery and isolating switch that has battery 1 / battery 2 and battery both positions.
While parked in my driveway, with the isolating switch turned to the "off" position, the house battery is running down from fully charged to around 3 volts in the space of a week, and I'm just trying to track down why that might be.
Attaching to the + terminal there's a direct line (fused) from the stereo, the main red cable that comes from the battery isolation switch, and one other skinny wire which I haven't traced the destination of as yet.
What's the general principle in wake boats / Tige for power & battery wiring?
Should absolutely everything run through the isolation switch, or should some things alway have a direct non-switched connection, and what would they be?
Are there any wiring diagrams / schematics for these boats?
Obviously the boats get fiddled around with a lot as they get different modifications / additions over the years.
I have an owners manual, but that is super basic and just talks about general use of the boat - there's nothing that I've found here or online that's like a owners handbook in a car which tells you what every light and switch and feature is & does.
Thanks...

[chpthril]

Sounds like there is a substantial parasitic draw. Two thing I would suggest. Identify the draw and resolve and then relocate ALL the non-essential loads (positive cables) from the batteries to the output terminal of the main switch.

On your boat, the only non-essential load is the brown/red auto-bilge wire. This one will stay connected to the battery. Everything else thats not a battery cable go to the switch, needs to be relocated to the switch. So when the switch is off, EVERYTHING is off, except the auto bilge can still run.

If everything switched off, no lights on or no sounds of a pump or blower going, then you can test for a draw. If its a light draw, say under 10A, most digital volt/ohm meters have a draw test mode. If its a higher draw, it may be too much for a small meter. You can try an amp clamp. You can also use an old school test light with an incandescent bulb. Or if you disconnect a cable and then get an arc when you reconnect it, that can indicate a draw. Just note, amplifiers have capacitors that will cause an arc when reconnected, this is normal and does not mean they are the draw. If you disconnect and quickly touch the cable back to the battery, the CAPs should still be charged. The head unit might do the same, it will have a small cap and also memory.