Ebay horror ...

Of course, like most of my answers to this list it will likely be corrected later on, here's a quick answer: Keyboard (1 letter press = 1 signal line) goes to... -> Arbitrary plugboard (''fixed'' rotor) -> Rotor: N signal points in, N out in scrambled order, angle dependant -> Rotor, with diff. scrambling AND angle -> Rotor, again -> Light array (1 signal line = 1 Illuminable Letter) The rotor as you may guess increments with each keypress. Later improvements included a fourth rotor and a reflection arrangement which apparently allowed each rotor to pass the signal both to its right AND to its left without ever having crossed wires (neat). It would reach the far wall and then be sent back eventually to the rotor origin. A wire cross anywhere would cause non unique mappings, IE 2 letters out at once, which was designed out. John IIRC.