A modular plug board system is disclosed for interconnecting an array of parallel cards in a card cage. The cards are pluggably connected to the IO circuit board of a machine to be programmed by the plug board system. A rear board of the plug board system is divided into sections which impinge one another in side to side relationship. The sections are pluggably connected to corresponding cards and are individually removable from the plug board system to allow for individual removal of the cards from the card cage and from pluggable connection with the IO circuit board. One or more cards may be eliminated from the card cage to allow for discrete wire or cable connection directly from the IO circuit board to an appropriate section of the plug board system.