It is theoretically possible but not practical. If you look at my sketch, it will work but LOAD B must be completely isolated from chassis ground. That is impossible with most typical automotive accessories, radios, motors, lights etc. as they are internally grounded and use the chassis for return.It would require that everything on the LOAD B side be a two wire circuit. Imagine the confusion five years down the road when you or someone else is trying to do some work on this circuit.