Apple ColorLaserWriter 12/600PS - Manual (Page 158)

7 Insert the locking connectors.
The locking connectors secure the printer to the feeder.
8 Replace both paper cassettes (one goes inside the printer, the other inside the feeder).
9 Connect the feeder’s short power cable to the printer.
Insert the straight end of a
locking connector through
the foot of the printer,
securing it to the locator point.
133 Installing Options