My assumption is that you are using a single pole disconnect switch between the battery and the rest of the car. Somehow you are trying to also disconnect one of the field wires to the alt to stop it from generating electricity
yes I am using that to disconnect the battery to the car. I also have the charge wire (largest black wire) from the alternator to the battery side of the disconnect switch so that when the switch is off the alternator is cutoff from the car circuit and the car will die.
My understanding is that the field wires are the 2 smaller wires connected to the alternator (blue and green I think) but I have not disconnected those are modified them.