I have wired the rear mounted battery cables today from:
The battery mounted in the trunk to,
The interior dash cut off switch to
The exterior cowl mounted cut off switch to
The solenoid under the hood.
The battery/ignition current feed wire from the regulator will be redirected to the hot/current side of the interior cut off switch.
To complete this circuit:
A New wire will be fixed to the cold side of the external cut off switch and then fixed to the ignition
This will allow the battery/alternator circuit to still function correctly while isolating the rest of the electrical system when either cut off switch is OFF/open. Both cut off switches will need to be ON/closed for the car to run.
But either cut off switch can be switched off to stop the car.
The Zener diode (as mentioned by Parnelli) will be also added for safety to the 12v hot side of the generator light wires(the engine off hot feed) to allow current to travel from Regulator to the Gen' light only, but not back flow through the other 12v wire connected to the generator light when the engine is switched off.
If you can be bothered reading all that confusing blurb!
Here's the pics
Still need to fit wire retainer clips
The original Monte Carlo Rallye cars had the battery wire fitted inside a rubber tube as this picture shows.