AT&T System 75 Wiring Diagram page 262

FIRST
APPEARANCE
TO GROUND
TERMINALS
Figure 4-37. Ground Wiring Example (Five Telephones Used for
Emergency Transfer and as Normal Extensions)
Telephone Installation
Install telephones assigned to emergency transfer as follows:
1. If ground start is required, do Steps 2 through 9 to install the ground
start switch; otherwise, go to Step 10.
2. Remove cover from 551A key.
Miscellaneous Wiring Installation
WHEN USING 66-TYPE HARDWARE
TO GROUND
TERMINALS
WHEN USING 110-TYPE HARDWARE
LAST
APPEARANCE
4-65