Very close, Twisted, but incorrect. The common control lead (A1) is the orange/white, not white/orange.
Also, Western Electric (AT&T) stopped using common grounds for the lamps on 10/20/30 button sets pretty early-on, but ITT (Cortelco) and Comdial (Stromberg-Carlson) continued to provide a copper strip that tied all of the lamp grounds together. I didn't work with Northern Telecom sets much (Logic 10 and 20), but the wiring was almost identical to Western Electric.
The 10 button phones pretty much used 2 1/2 pairs per line, one for the CO line T/R, one for the lamp (LG/L), and the half-pair for the "A" lead. Only one common lead ("A1") was required regardless of the number of buttons. With this arrangement, there were not many spare pairs to throw around for extra stuff, like transfer keys.
That's when we started stealing those lamp ground leads. It was amazing how much progress you could make by just having one extra single wire available to work with.
Man, you just lost the grand prize, a 2006 Hummer H2 and perfect 21-30 year-old women to fill every seat. You need to be more careful with your answers next time!
I am still impressed that you knew that much about a tried and true, yet dead technology.
If you want to see a 1A2 KSU, I will send you one if you pay for the postage.
