Lexmark 4I3 - Manual (Page 163)

Attaching a Serial Cable
CAUTION:
Make sure the machine is turned Off (O) before you connect
or disconnect the power cord or other cables.
If the machine has cables other than the power cord, you
must connect them before you plug the power cord into an
outlet. You must first unplug the power cord from the outlet
when you remove the other cables.
To attach a serial cable:
1. Attach the serial interface cable by pushing the connector into
the printer port.
2. Tighten the two locking screws to hold the cable in place.
Chapter 2. Attaching the 4230 Printer to Your Computer 2-23