The cable connecting from the motorhome to the car is a four wire cable. I would like to switch to a six wire cable so that I can charge the battery in the car as we tow. My question is wiring the car side of the connection. Obviously I need to connect the power lead to the positive side of the battery. My question is what do I need to do about grounding the car/battery relative to the motorhome. Terminal #4 on the connector is the Battery Charge lead. Terminal #1 is ground from the motorhome. Do I connect Terminal #1 lead to the car frame or do I connect it to the ground side of the battery?

Jim