Biohazard
How dare you, my good sir! Grandpa rocked an AM radio into the 21st century!
I believe you're referring to the toggle labelled "REAR AIR" which activates the factory rear window defogger. Interesting setup this as the blower fan draws air from the cargo hold through a 6 x 9 speaker grille.
Pistols at dawn then, Sir. Our seconds can hold our coats.
THAT is the Second Mod this '69 has that I wish I had on board mine. I have been thinking about fabricating an air funnel and blower motor to do exactly that. Love to see how yours is laid out physically and electrically. Flying one of these things in the spring, fall, winter, and in the rain- the rear glass becomes useless- that, along with the giant blind spots and the single mirror on the driver's side. . .well, let's say that a bunch of people over the years have had me try to occupy their lane and recreate that physics experiment. . . .
The oval holes with the 6x9 speaker grills I saw in one pic suggested that stereo might have been added on "Day 2". . .along with the sidewall coverings.
Great car Sir. I might suggest you consider EZ Cool insulation from lowbucrod.com. Check out the Aussie testimonial! I have that down double from the plenum all the way to the trunk area, single on sides and top- and have put in place a bit of a water vapor barrier between the rear roll down window area and the trunk area to control some of that excess water vapor that steamed over my rear glass all these years. . .along with a flapper valve of rubber over the defroster slot for now.
Mine showed up in my life new (demo car) from Solok and Turner in Pasadena TX in Spring 1967; I was 9. Learned to drive in it, HS, college, first honeymoon; never let it get away from me. She is getting the rebuild and improvements she has always deserved. . . .it will be my time machine.
Enjoy!
Mike