Kid,
That is part of a modification that was done to the ventilating system. The placard below the knob reads "PULL FOR FLOOR". Pulling the knob directs air to both foot wells. It is referred to as a "Field Fix". This mod removed the duct from the center defroster vent and added two ducts to the two foot wells. It was more involved than that, but that was the end result.
John
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