This knowledgebase article provides information about the different connectors on the pneumatics board of the 6890 GC. There are (5) distinct connectors on the pneumatics board to plug in EPC Modules. Front inlet, front detector, back inlet, back detector and auxiliary manifold / module.
Pneumatics Board - Part Numbers
G1575-60010 - (6890A / 6890 Plus)
G1575-60015 - (6890N)