AT&T System 75 Wiring Diagram page 243

CHAPTER 4. STATION WIRING
Figure 4-25. 574-5 Power Transfer Unit Option Switches
When ground start trunks are used, the transfer unit automatically
provides ground start for each trunk without requiring any special wiring
at the telephone used for emergency transfer service.
Figures 4-26 and 4-27 shows the connections on 110-type terminal
blocks and 66-type connecting blocks, respectively, at the trunk/auxiliary
cross-connect field for a telephone used only for emergency transfer.
Figures 4-28 and 4-29 show the connections on 110-type terminal
blocks and 66-type connecting blocks, respectively, at the trunk/auxiliary
cross-connect field for a telephone used for emergency transfer as well
as a normal extension.
4-46
TRUNK TYPE SWITCHES
LOOP START
GROUND START
BOTH SWITCHES MUST BE THROWN
FOR TRUNK TYPE
1 1 AND 2
2 3 AND 4
CIRCUIT
3 5 AND 6
NUMBER
4 7 AND 8
5 9 AND 10
USE SMALL SCREWDRIVER TO MOVE SWITCH
OPTION SWITCH
1 2
SWITCHES