Apple PC Compatibility Card (Installation) - Manual (Page 75)

Connecting two monitors
If you connect two monitors, you see the Mac OS environment on one and
the PC environment on the other. You can use any combination of Macintosh-
and/or PC-compatible monitors (with the proper cable adapters, available
from your monitor vendor or Apple-authorized dealer or service provider).
To use two monitors, you connect one to your Macintosh built-in monitor
port. Then you plug the middle connector on the loopback cable into the port
on the PC Compatibility Card, and connect the second monitor to the short
connector on the loopback cable.
Multiple-scan monitor: If you want to use a multiple-scan monitor from a
manufacturer other than Apple to display the PC environment, you also need
to use a VGA-to-Macintosh adapter (available from your computer vendor).
You connect this adapter between the monitor’s cable and the short connector
on the loopback cable.
This connector (“middle connector”)
attaches to the PC Compatibility Card. This connector (“long connector”)
is left disconnected.
This connector (“short connector”)
attaches to your monitor cable.
75 Installing the PC Compatibility Card in a Modular Desktop Macintosh Computer