Complex sentence: The keyset cables were typically routed to a wiring closet or wiring panel where the Key Service Unit (KSU) was installed and were terminated on a 66 type punch block, typically a model 66M1-50.
Split into simpler sentences: The keyset cables was typically routed to a wiring closet or wiring panel where the Key Service Unit (KSU) was installed. There it was terminated on a 66 type punch block, typically a model 66M1-50.