Father-Son 1974 Duster Project

17 Again said
While I was taking the bottom rear glass stainless trim off the back glass so I can get ready prep the trunk gutter, I noticed this rear defrost vent boot. What supplies the warm air I wonder?

If I'm not mistaken, a short piece of hose would go to a fan motor that mounts in the speaker hole. Draws it's air from the interior of the car.