[Bob Mulry]

It doesn't matter if you disconnect the Positive or Negative cable with the disconnect switch or where the switch is located...........

If you have 2 batteries (1 in the front of the car and 1 in the rear of the car), the cables still have to connect to the disconnect switch......

Even with the switch off, in the event of an accident, there would still be cables that run from the batteries to switch, that if damaged would create a short circuit.............

If using a disconnect on the ground or negative side and the cable was damaged and/or crushed between the battery and the switch, the entire car would remain hot and not controllable by the disconnect, as in the fuel pump, fan, ignition would continue to be energized.

If the hot or positive cable gets damaged and shorts between the battery and the switch you have a dead short and a potential fire

The only safe way to wire 2 batteries, 1 in front and 1 in rear, is to use a continuous duty, high amp rated relay located at the front battery and controlled by the disconnect switch, which also controls the rear battery...

Just my 2 cents,
Bob Mulry


PS:
Not as safe as you thought it was...