16 Module Expansion Chassis with power supply for Mesa 16 Control. These are passive, bidirectional relay-based Multiplexers, connecting one of up to 16 multiwire signal groups to a single signal common. Nine, fifteen or twenty-five wires are switched simultaneously. These pre-wired chassis hold RS Switch Modules built with D9, D15 or D25 style connectors and switch 9, 15 or 25 wires.

link to switch module selector