With direct current the circuit has to be completed back to the source. If the negative to the car/truck battery is disconnected how is the current returning to the battery? I agree that there is a ground to the coach through the attachment of the toad wiring, but as mentioned above, where is the current coming from? Maybe through the coach batteries, but this has nothing to do with the toad battery. If this is the case the same problem would exist disconnecting the positive or both. Maybe I am confused, but I believe this is the way DC current works.
