AT&T System 75 Wiring Diagram page 258

Installation
Make connections as follows:
1. At cross-connect field, connect a jumper from one DID make-busy
lead to the TK terminal (first appearance) on the yellow emergency
transfer row/connecting block (Figure 4-35).
2. Connect a jumper from the other DID make-busy lead to the ST
terminal (first appearance) on the yellow emergency transfer
row/connecting block.
Installing the Z1A Emergency Transfer Unit
Install the Z1A emergency transfer unit as follows:
1. Mount emergency transfer unit on the wall to the left of the
trunk/auxiliary cross-connect field. Mount additional units on the
wall below the first one in a vertical column.
2. Connect a B25A (for 110-type hardware) or A25B (for 66-type
hardware) cable from the emergency transfer unit to the connector
associated with the yellow emergency transfer row/connecting
block in the trunk/auxiliary cross-connect field.
Installing Telephone Associated with Z1A Emergency Transfer Unit
Trunk/Auxiliary Field Connections—Telephone Used Only for Emergency
Transfer
Install telephone as follows:
At trunk/auxiliary cross-connect field, connect a pair of wires
1.
between the -48V and GRD terminals on the yellow emergency
transfer row/connecting block to the EM TRANS RELAY PWR
terminal (Figures 4-31 and 4-32, respectively for 110-type and
66-type hardware).
2. Connect CO trunk leads from the purple field to TC terminals on the
yellow emergency transfer row/connecting block for each trunk.
3. Connect CO trunk leads from the green field to TK terminals on the
yellow emergency transfer row/connecting block for each trunk.
Miscellaneous Wiring Installation
4-61