What's the button thing/switch on the dash for?

??? My 65 had neither a toggle switch, nor a plug, nor a hole there originally. I did put a toggle switch there in the early seventies for the driving lights I was running at the time. Now have a toggle switch hooked to nothing, just to plug the hole.

Things have been added to these cars in the 57 years since they were built. I don't think the switch in the picture is factory, but every now and then I find out about something that was rare when new, but did exist. So ???