Battery cut off switch
No need for all that extra stuff.
X3 on the 8ga. wire to the Battery side of the cut off switch.
Take the "power" wire that runs from the alt to the bulkhead and throw it out. Now run a new 8 ga. power wire from the Alt. to the battery side(OFF) of the cut off switch. IT WILL CUT THE CAR OFF. If you run the wire to the (ON) side of the switch then it wont shut the car down. I have never failed tech with mine hooked up this way.
Not saying the other ways don't work but not sure why would you go through all that wiring to do the same thing.