Yes, the 4 wire SMI system had a break-away system that was wired from the toad vehicles battery to the break-away system switch. That way the unit has power when disconnected from the r/v's power supply
In your description of the SMI unit you state that the unit uses the toad's electrical system. I had the 4 wire SMI unit on a 1999 Fleetwood Bounder 34' and was towing a 1999 Honda CRV. The electrical source for the 4 wire SMI unit was the Motor Ho...