Epson TM-300A Operator's Manual page 14

<TM-300PA/PB>
Connect the interface cable according to the following procedure.
Turn off the printer, and the ECR (host computer).
Plug the interface cable connector into the interface connector on the printer.
Squeeze the wire clips together until they lock in place on both sides of the
connector.
Attach the ground wire to the ground connector on the bottom of the printer.
Plug the drawer kick-out cable connector into the drawer kick-out connector on
the printer. (When removing the drawer kick-out cable, press in on the
connector's clip and pulling out.)