I am just guessing here, but thought I'd give this a go as a suggestion. Back in those days, many manufacturers' 1A2 products were often designed to mimic the styling of Western Electric's Comkey sets. With that said, they didn't have traditional ringers or buzzers. The associated pairs (yellow/slate and yellow/orange, respectively) were used for other purposes on electronic sets. Again, this just a guess, but I'd start with the yellow/orange for power. I'd check for continuity on both of these pairs, plus all of the violet pairs on the first binder. Then, using a 24VDC power source with the lowest Amperage fuse you can get, connect it to the pairs that give you continuity to see if you can at least get power to activate the features. After that, the rest might be easy.

Ed Vaughn, MBSWWYPBX