Around 1960, somebody my father knew at the Harrisburg AMP factory gave me a chunk of plugboard bandsawed from a scrapped computer or industrial controller, because he knew I’d enjoy it:
He was right.
I spent months rearranging those little cubes (some with cryptic legends!) into meaningful (to me) patterns, plugging cables between vital spots, and imagining how the whole thing worked:
Long springs ran through the notches under the top of the blocks to connect the plug shells to circuit ground. The ends of the steel rails (still!) have raw bandsaw cuts, some of the blocks were sliced in two, the tip contact array behind the panel wasn’t included, and none of that mattered in the least.
Only a fraction of the original treasure trove survives. It was absolutely my favorite “toy” ever.
Quite some years ago, our Larval Engineer assembled the pattern you see; the hardware still had some attraction.
I’ve asked Mary to toss it in the hole with whatever’s left of me, when that day arrives …
The Smell of Molten Projects in the Morning 
Nice, can’t say I’ve ever seen those before. Sort of like an industrial litebrite or battleship for electrical signals.
They went out of style a long, long time ago! [grin]
I suppose assembling plugboards went along the same lines as weaving core memory ropes for the Apollo Guidance Computer: sliding colored blocks between those steel rails according to a prescribed pattern.
One of these days I must disassemble and rebuild what’s left, although the nostalgia might knock me over.
I recently bought a 16 pole rotary cam switch for a project. It was obvious it was never used and equally obvious something lived inside it at some point. I stripped it down for cleaning and what came out can only be described as industrial, grown man Lego :)
Each segment has a cam which obviously starts in life as a blank and gets milled to appropriate timing profile, all segments are stackable, all is good quality plastic (determined by not crumbling apart even though it was made 30 years ago), the front has a ratcheting sprocket that determines position of detents, manufacturer has switching schemas for every type they built, basically you can build any switch imaginable.
Lego, pure and simple. Sorry I can’t post a picture here :)
Once upon a time, I had a map from a nap-of-the-earth guidance system: a relief map wrapped around a fist-sized aluminum cylinder. Apparently, a stylus traced the current position on the map to set the altimeter and keep you out of the trees. Lovely bit of metalwork …