What is it you need to know? The lines are 3 pair each starting with the wh/bl. Buzzer leads are the yellow green, common bell is yellow slate. If memory serves the co lines are on the bottom. There will be others who can remember these things too. I've got some old manuals...somewhere!!... You'll need line cards and you'll need an intercom card, if you want intercom. I think most everything else is in the 551. You'll only have button and buzzers unless you add a dial intercom.
