grounding heater box 68 cuda AC equipped

Looking at the illustration in my service manual , it shows a ground strap connected to the body, but it does not show where/what its attached to. This car WAS originally an AC car but all that equipment is long gone , including under dash vents and evaporator. When i pulled the box there was a brown wire screwed in to the "W-shaped" clip that holds down the two tubes from the heater core, but it was not attached to anything on the other end. I assumed it might be some kind of ground strap. Yes?? No??
What is the purpose for grounding a heater assembly? As near as I can tell since the core is mounted in the fiberglass box, how could that ground the blower motor if that's what its for?
Thanks in advance,
Neal