This is getting very confusing. The extra white and green wires on the actual battery negative post are a battery sensor, per the dealer’s service department, those wires do not connect the battery to ground. If a wire that small did connect to ground it would melt quickly. So, you can disconnect the black wire at the fire wall connection. But one of the lower mechanics still said no. The other four and the lead mechanic said yes!
I am having a two position battery disconnect switch added to the left of the battery just below the front window where there is space to install it. The existing black wire can feed the switch and a second wire can then be added between the switch and the existing bolt on the firewall.
Just to be safe, I’m having the dealer cut the battery monitor wire and install a simple two wire connection outside the battery box. I can now throw the disconnect to the off position and unplug the sensor. That definitely takes care of the battery’s black wire.
I found a local RV dealer who will do all of the work to convert the car to flat towable, none of this you connect the base plate and you connect the wire harness. The RV dealer is going to use a wire harness that uses diodes to insure that current and ground from the motor home does not feed back to the car’s power system and he is also going to install a second power outlet (cigarette lighter) under the dash near the brake pedal. That way we can use a standard braking system and it will have its own power outlet direct to the motor home. The cost is not nice, a little over $4,000 including all parts and labor, but we are getting the best parts available, including a tow bar that does not require a drop hitch. I can just see us going over a driveway or incline that dips the rear end close to the ground and breaking the drop hitch, we no longer have to worry about that.