Heater box plug/ground wire

Hello. Working on a 68 barracuda with a 318, No AC, heater only. Long time ago i disconnected the plugs to the heater box sou i could replace the heater core. I can't figure out where this brown ground? wire goes? here's a pic where it would go somewhere on the heater box, does that go right on that left screw for the resistor? and the other end is a length of wire with another ring terminal, where does that hook up? on the dash somewhere, or on the body somewhere?