The pairs are wired right across the T & R of each line. Parallel, not in series. The unit uses voltage detection to determine on-hook, off-hook, or ringing. There is a separate pair for a transformer to power it. (I think). I will check to see if I have a BSP.
Does yours still have the 25-pair cord, and the amphenol at the end? From memory, the transformer is wired at the plug, not the unit.
