Closeup of the internal line switch. If the switch is pressed down a set of contacts is engaged which can be wired for signaling another station. 631C is the part number of this switch.

Closeup of the exclusion switch mechanism

Underside of the housing. The white plunger on the left interfaces with the exclusion mechanism seen above. On this phone, when the white plunger is pulled up, the line which is not selected is put on hold, enabling the user to switch lines without loosing the call.

Network manufactured: June 19, 1979

Circuit board under dial

Wireing diagram