The location of that connector in SmartWillie's post is where the breakaway switch is installed on my car.
I opted to not use the wiring harness to the smart car's rear lights - instead I use magnetic tow lights connected directly to the motorhome and attached to brackets I install in the tow hook locations on the rear of the car. This had no effect on the electronics of the car, no need to use the car's power, and only takes several minutes to hook up.
Legalities aside, you might also consider that the car is so short and narrow that the motorhome's rear lights are easily seen by any following vehicle and that any vehicle following would never come as close as the towed car anyway.