They were used to "broadcast" everything that was needed to assemble each particular car to the far corners of each sub-assembly area of the assembly plant.
The trim shop where the front seat(s) were assembled "heard" the broadcast.
So did the trim shop for the rear seats.
So did the assembly area for the dash frames / gauge clusters.
.........and on and on, thus the name "broadcast", the information needed was broadcast to everyone that needed to know.
If you liken it to a radio broadcast of the news where everyone hears the same thing at the same time, that is pretty much how it worked inside the plants. Each assembly section "heard" what they needed to know and did their part.
The only difference was that the "broadcast" was printed on paper so they could read which each car needed and what they had to do to make it happen. Each sub-assembly area had it's own printer.
