There are two gray plastic fixtures with wires attached that are installed
out of sight, just up under the lower edge of the dash, at the outermost
edges on both sides of our '78. The best way I can describe them is: they
resemble miniature versions of the 'scoops' that you might use to shovel
out pet food, or flour, or something of that nature.

My assumption is that they're interior courtesy lights, because they have
metal 'sockets' at the rear, seemingly for push-in style bulbs. These have
no bulbs in them though, and the fixtures seem a little large for lights--
but I can't figure out what possible other purpose they could serve. Plus it
seems a little strange that GM would have used plastic to house a heat-
producing item like a lightbulb. But then again...

Can somebody please enlighten me (you should pardon the expression)
as to what these fixtures are for? And the right side one is dangling down
by the wires, unattached to anything right now--so any guidance on how
that should be reattached would be very helpful...

Ted, sound like the under dash lites. The drivers side goes into a molded in depresson in the bottom lip of the dash kinda between the ductwork. It's awful hard to get it snapped in. tho. Pics?...got pics of everything!  Mike mkapp787938964.4961689815

Them's the very things, Mike--and the pics you provided show me just
how that right side fixture attaches to the lower panel. So armed with that
info, it'll be back beneath the dash for me...

Thank you for the fast help--it's much appreciated!

(and all I can say is: wow! You really do have photos of everything, don't
you? I just may take my cue from you and document this shark inside and
out...you were smart to have done that. My favorite photo of yours
though is that shot of all four beauties, lined up in a row...)

Mike's the MAN on the '78-79 cars, no doubt!!