IBM 3270 Maintenance Manual page 260

1.
Refer to the figure below and install the wrap
plug on the modem end of the IBM
Communications Adapter Cable.
2. Press Enter to begin the test. The test may
take up to 15 seconds.
IBM Communications Adapter
Wrap Plug
DID YOU RECEIVE A MESSAGE
INSTRUCTING YOU TO INSTALL THE
WRAP PLUG ON THE ASYNC ADAPTER?
NO Go to page 3-1100-7
YES
October 1984 3-1100-5