Abstract: In general, an electronic control module includes a module frame adapted for swingable mounting to a rail member. The module includes a plurality of bus conductors constructed and arranged to engage the bus conductors of adjacent modules when mounted. The module also includes a plurality of electrically-conductive pads for engaging a circuit board which is attachable to the module frame. Terminals are included for the connective termination of external wiring. The module is swingably removable from a rail member while yet avoiding movement of a module which may be mounted adjacent thereto. The invention is particularly useful for the construction of electronic digital communication systems used with heating, ventilating and air conditioning equipment.