Wayne,,,I think it is time to take another owner survey. My 58 D isn't home so I can't check it tonight but I recall the defogger inlet and motor mounted in the center with the appropriate grille and the radio speaker mounted outboard(left side). I believe I checked another D and it was different with the speaker on one side and the defogger on the other for symmetry. I know that my installation wasn't switched since the telltales of the lock washer scratching the underside of the shelf panel provides evidence. I have a feeling that installation will vary depending on dealer install or not. Mine was a factory option. Responses should indicate factory or dealer installation and standing behind the car is the radio speaker in the center or is the defogger motor and grille. Marv [Non-text portions of this message have been removed]