The way to terminate a 1200-pair cable is the same as eating an elephant: One bite at a time.

Historically (and in the US, at least), telephone wire has been organized into chunks of 25 pairs each, with each pair of wires having a unique color code.

And every 25 pair cable in a given system has the same set of wire colors.

And these 25-pair chunks are easy to terminate on (say) a 66 punch-down block. It takes some time to learn how to get good at it, but not as much time as one might think.

Those 25-pair chunks are organized into 5 different body colors, each with 5 different pair colors.

We're all familiar with the colors of 4-pair cat5 and friends; that's just the first 4 pairs of wire of a 25-pair chunk. (We can tell that they're the first 4 pairs because they all have the color white in common with eachother.)

So, the order for a 25-pair cable is this:

   First, the white pairs:  Blue, Orange, Green, Brown, Slate. 
   Then the red pairs:  Blue, Orange, Green, Brown, Slate.
   Then the black pairs:  Blue, Orange, Green, Brown, Slate.
   Then the yellow pairs:  Blue, Orange, Green, Brown, Slate.
   Then the violet pairs:  Blue, Orange, Green, Brown, Slate.

Done. A 25 pair cable is terminated.

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Larger cable are also organized into 25-pair chunks. The colors of the binder strings wrapped around each 25-pair chunk identify it.

This works for cables with up to 600 pairs.

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1200-pair cable just consists of two 600-pair groups, with each group wrapped in its own colored binder

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So to begin terminating a 1200-pair cable, first you identify the first group of 600, based on the color of outermost binding wrap. Now the 1200-pair problem is only a 600-pair problem.

Inside of that group of 600, find the first chunk of 25 (the white-blue one). Now your 600-pair problem is only a 25-pair problem, and terminating 25 pairs is easy.

So terminate all 25 pairs, and then move onto the next chunk of 25 (white-orange).

Keep doing this until you've worked through all 24 chunks of 25 pairs in that 600-pair group.

And then just do it again for the other 600 pairs.

[]: http://cityinfrastructure.com/OutsidePlant/Webfiles/colorcod...

They had splice tools, but you were still threading cables to each other by hand.

The model train club I used to be a member of was full of old telephone guys, and they'd share old stories

Yeah - there are colour codes you can use to find the pair that you want to connect, they are arranged in a mystical system of binders. It's like a map.