AT&T System 75 Wiring Diagram page 141

CHAPTER 3. EQUIPMENT ROOM DESIGN
(5) purple labels to identify connections to dual-purpose
emergency transfer stations (Figure 3-40).
Labeling 66-Type Connecting Blocks
The cross-connect field is color-coded to identify system wiring as
follows:
Green—Leads to CO
Purple—Leads to switch ports
Yellow—Leads to auxiliary equipment and miscellaneous switch
leads
Blue—Leads to information outlets
White—Leads from the cross-connect field to the satellite
locations (3-pair).
A permanent felt-tipped pen can be used to write the lead designations
on the 66-type connecting blocks (Figure 3-41). Table 3-G shows the
lead designations for the switch port appearances at the cross-connect
field, and Table 3-H shows the lead designations for the auxiliary
circuits. Any time these leads are cross-connected to another connecting
block they should also be labeled at that block.
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