What this is doing
Start at top left the blue "cut" wire. That is the original "ignition run" wire coming out of the firewall/ bulkhead connector from the ignition switch, and out into the engine bay. It originally fed several things "under the hood" depending on the car model, year, and accessories.
At the very least in 72, it feeds the igntion system, the blue alternator field, and the power to the voltage regulator. It may also feed the electric choke and some smog control doo-dad
That original circuit is subject to voltage drop problems which is why the idea of a relay or continuous duty solenoid. The key turns on the solenoid, and the solenoid then feeds the loads thus relieving the wiring.
NOW Notice that in this modification, the "cut blue" coming out of the bulkhead is wire to the rear, to one terminal (small) on the disconnect, and BACK up front to feed the solenoid. The key switch is turning on the solenoid through the disconnect, and allowing the thing to operate. So when you pull the disconnect, this drops out the solenoid and kills BOTH ignition power, and the voltage regulator and field power. It can not run on
ALSO NOTE that you can easily create a sort of anti-theft by hiding an extra toggle switch in the solenoid circuit, OR IF YOU MOUNT the disconnect inside the trunk, and operate it with a push-rod, you can easily create a rod-inside-a sleave set up where the switch can be "pushed" off, but cannot be turned back on with the pushrod. You have to unlock the trunk to re-power the disconnect.
