Flickering head lights, what am I missing

There are only two basic ways to get a disconnect to kill the engine. If you use a 2 post disconnect, you must run a great big separate charging wire from the alternator back direct to the battery. But THAT is what all the controversy is about, because it leaves a great big wire to the battery!!! And can defeat the purpose in a crash

The second way is to use a 4 terminal disconnect and break some circuit that will either kill the engine or drop the alternator VR / field so it won't charge. Then the engine will stop