carrier master t-stat

[white6294]

i had a 4 zone control board carrier that is about ten years old, it had temp readings in every room, and one t-stat that controlled all of these zones, and the programs for these zones. i sold the HO new eqiupment 19seer 2-stage, and went looking to replace the old t-stat with a new one as part of our package but found out that we coulndt without replacing the zone board also. there were 2 bus strips on the back of the t-stat, one with r,g,y,w,, and another with r,g,w. but my question, i got the 35 page intrustions from my service man., and all i had to do was change one of the settings in the t-stat to make the y2 in the board energize, how was the singal getting from the t-stat to the board?
i will get model number monday if needed.