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

That particular wire grounds to the sheet metal behind the kick panel. At least, that's where it connects on my 68 Dart. I'm not exactly sure of the reasoning. Maybe the water passing through the heater core creates a small charge?

The blower motor should have it's own separate ground wire to the firewall.

thanks