is this just a cable with it`s housing going to a control valve with a push/pull knob mounted on the inside the cab? so what i'm thinking i'll need is a manual valve with the right diameters (in and out) to splice into the hot coolant line on the engine side of the firewall to block off the inflow of hot coolant to the heater core that will (hopefully) eliminate extra heat inside. if so, would additional insulation on the undercarriage be necessary?