How did the Times Square "zipper" work in 1928 without computers?

Answer 1

Probably a paper tape was used to trigger electrical contacts for individual lights. As the tape moved across a reader holes punched in a coded pattern would trigger specific lights on and off.

Think Player Piano but triggering lights instead of keys

Another possibility is that a large paper tape was used to display the message by shining light through holes in a black paper strip. This would operate like a super sized light bright but it would be a low tech solution .

Answer 2

I don't know, and have been unable to find any information on how it worked. However, I suspect that it was largely mechanical, likely using a punched paper to control the switching on and of of the light bulbs, something like a player piano. Player piano technology was well known then, though the popularity was starting to decline.