AT&T System 75 Wiring Diagram page 153

CHAPTER 3. EQUIPMENT ROOM DESIGN
Routing Cables Using 66-Type Connecting Blocks
Figures 3-48 and 3-49 show the cable routing pattern through the cable
slack manager for a single cabinet installation with the cables routed
from the top and bottom of the 66-type connecting blocks, respectively.
Cables are routed through the cable slack manager in either the cabinet
or wall troughs. When needed, the two center troughs can be used.
Port cables are routed through the cabinet trough for parallel runs.
Station cables should use the wall trough. After the cabinet and wall
troughs are filled, use the center trough.
3-70