Rodney’s idea is very clever, putting a relay on the 120vac charging cord would work for any future charger upgrades as well. Plus, there’s no parasitic power draw when unplugged.
The only thing I’m not certain about is how the Ground interconnect works on the older gem cars. Is the GEM car interconnect wire live voltage 12v, 72v, or ground? What does it “ground” to? If the car interconnect circuit is closed, is the car enabled or disabled?
Sorry. I’m missing that piece of the puzzle. If I had my car at home I could just measure it.