AT&T System 75 Wiring Diagram page 158

Equipment Room Hardware And Cabling Installation
Installing Control Carrier Outputs Cable
The control carrier AUXILIARY connector outputs include the following:
Alarm monitoring for the AP and auxiliary cabinet
(7) dc power (-48 volts) sources for emergency transfer units
(3) dc power (-48 volts) sources for remotely powering two
attendant consoles and one executive voice terminal adjunct (not
provided on System 75 XE)
The INADS trunk connection location.
For the System 75 XE, access to a relay contact is available to
actuate a light, bell, or similar type customer-provided alarm
device. The relay can be administered to make contact when a
major, minor or warning alarm condition occurs in the switch. The
circuitry required for this feature must be provided by the
customer. The device connected to the alarm leads must not
exceed a rating of more than 100 volts at ¾ amps.
A 25-pair cable connects the control carrier AUXILIARY connector
(Figures 3-51 and 3-52) to a 66-type connecting block/110-type terminal
block in the yellow field of the trunk/auxiliary field.
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