Master shut off switch charging problem

Mattax said:

I'm not clear why its important to be hooked to the ammeter in this situation.

If you want to use the ammeter then my suggestion is use it only for battery charging. Then it will read correctly, and not be carrying extra loads.
And if you want to do it with just one fusible, then something like this should work. Use a grommet through the firewall (or some other substantial firewall feed).
The MSD heavy red wire can connect at the terminal as can the fuel pump.
View attachment 1715539630

the other guys may see faults or drawbacks here.

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Thanks Mattax, it’s not the ammeter I care about, its power to the fuse box. I do like in the schematic running the ground side of the cv relay through the master switch. That will cut down on a lot of wiring.
I answered my own question about relay current draw, it’s about 1.3 amps.

OK.
I'd say if you're not going to use the ammeter, then don't run any power through it.
In that case, hook a voltmeter to the ignition run (key on) at some convenient location.
(You could also do that in addition to having an ammeter.)
But my point is have something that provides an indication of electrical conditions.

I was considering that, I like to know if the charging system is working. Idiot lights are for chevies.

Here’s an update on this project. I put a painless 250 amp cv relay in the alt - batt. Line. I use a Summit kit that has a #6 wire and 200 amp fuse. I ran the wire through the relay and to the terminal between the front and rear batteries. I power the relay with the same ignition wire feed that turns the m s d on and off which is only hot when the key is in the run position. I then ran the ground side of the relay through a Joes four post Shutoff switch.
I put the fuse in the front battery + line and I plan on adding one to the rear + line between the batt and shutoff switch. One of the other members mentioned that in A crash if one of these lines that are still hot after the shutoff is killed shorts out, the fuses will blow. Great forward thinking there, thank you.
Now it shuts off with the switch and I have 14+ volts at both batteries, slightly less at idle. Almost time to go racing!