As I dive more into the electrical stuff, I learn more/confuse myself more.

Correct me if I am wrong, but with the 40a ext alt, if you turn off the power supplied to the field generator, the alternator will not make power(5A line on 5e schematic). If you break the connection between the alternator supply line and the bus/battery(50A line o. The schematic), the alternator will still be making power with no where for that power to go which damages the alternator.