67 dash question

[kgmunro]

I bought a 67 cst pickup this past summer for resto, it is the same make and model of my first truck so I am very excited. The truck is solid, still has the original paint on the foot areas so minimal rust repair is needed, only rockers.

I was looking at the dash yesterday and saw a switch I do not remember seeing before.
It is a silver push button looking type switch that sits in the hole to the right of the heater controls, I can not try it because the truck is in pieces and needs repair before hooking up the battery...any ideas?
Maybe it's something someone added but I do not see any extra stuff on the truck.
I forgot to take a picture so I can not show it right now but will try to remember next time I am there.