ID mystery circuit in 66 Barracuda

When disassembling my 66 Barracuda i found a 'mystery' circuit in the passenger footwell. Picture is attached. It is a single light green wire with a male blade, bound to a black wire that is grounded to the footwall with the heater ground wire. The other end of the bound wires was curled up in the footwell and had been cut together at the end. It is probably 1.5 to 2.5 feet of wire and cut at the end. Appears never to have been attached to anything, but it looks like some sort of power supply and ground to something.

I cannot find this wire on the wiring diagrams in the service manual or the commercially available colored chart. I would have assumed that it was a speaker, but the only speaker is in the top center of the dash and not the footwells or doors. Is this some option or something? My car did NOT have factory AC, but could it be a temp sensor or something associated with AC. Any Ideas?

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