Early Macintosh models used an RJ-11 (phone) connector for the keyboard.
Note that all models since the Plus use the Apple Desktop Bus instead, and
are incompatible with these cables and connectors.
Pin Name Comments
1 CGND Chassis Ground
2 KBD1 Keyboard Clock
3 KBD2 Keyboard Data
4 +5V
Connector Type: RJ-11 Connector, 4 pin male
WARNING: Macintosh Keyboard cable connectors are just like those used in
modular telephones, but the cables themselves are not. Never connect
these cables to your telephone, and never connect a phone cable to
your Macintosh.