I checked my owners manual and found where the Rear Windows Defroster switch is located on the 67-76 Dart. Below is a picture showing the manual having it as item 8 in the diagram, just to the right of the Map Light Switch, and there are some NOS switches located on ebay, a couple I've shown below, items 311378007064 ($49.99 + $4.54 shipping) and 311466027171 ($45.99 + free shipping) as of midnight (ET) on 11/2/15. But from looking at the switches for sale, they look identical to the Map Light Switch, as far as the actual switch goes, but I presume there would also be a plastic bezel identifying what the switch is for. I don't know this for sure, but I can't imagine it not having that.