Wiring problems of the 2009 Subaru Forester

While vehicle was parked outside, noticed side lights were on, car was not on. After entering the vehicle noticed a smell of burned plastic. Tried multiple ways to shut off the side lights, couldn't do it. Finally traced the smell of the burning plastic to the rear of the vehicle, by the lift gate, by the spare tire. The electrical cable that connects the vehicle to the trailer hitch wiring harness was burning and smoking. Disconnected it and the power failure stopped, by then the wiring harness had melted and wires burnt. Took photos of the wiring to show it, problem seems to be with the condensation in the area and moisture caused a short in the harness. Without intervening car could have caught fire and burnt down.