I don't know if this is relevant at all, but there was a push/pull button in our 78 Gremlin that would disengage the drive shaft from the rear differential. The car used to be towed by its original owner behind a Winnebago or something, and the push/pull button and the little doo-hickey it controlled would essentially put the car in neutral. Maybe something similar???
Could be. As my Eagles first owner use to pull it behind his motorhome and I have an odd little button in mine as well, though mine is at the bottom of the driver seat.