Battery disconnect switch

I don't have a harness yet, I will contact them. The way I understand it is that when you turn the vehicle off with the key, the efi and trans controllers are both disconnected when the voltage surge occurs so no damage happens. The surge goes into the battery, like it is designed to do. When the vehicle is turned off with a battery disco switch, the controllers are still energized but the battery is no longer present in the circuit. The surge is also still present though........