That red wire feeds the controller electronics 100% of the time. The other end goes to J1 Pin-5, which is used for some voltage comparisons, so if it is damaged, you may be getting some false errors, like a welded solenoid, which will put the cart in a reduced performance mode.
You are running tall tires, my guess 22", so the the stock controller is probably on its last legs. When it goes, replace it with a DCX400 and hold onto your hat.