Don't forget the "Privacy" feature, that used an MB-type relay inside each set. The -24Vdc that was required to operate the relay was sent to the sets via the Y/Br pair.

The privacy circuitry looked at the selected A-lead and if it was high, the T&R would be cut through. If it was low (already grounded by another off-hook user), the relay would exclude the T&R at the excluded station.

To add-on an excluded station, there was a Privacy Release key, which opened the A-Lead at the station who had seized the line first.

When the cleaning ladies mopped the floor, and the wax got in the Amphenols, smoke would ensue. Then the repairman who knew where the -24Vdc fuse was would make a few hours OT when the rest of the crew couldn't find it.

Been there, got the pay check.

Arthur P. Bloom
"30 years of faithful service...15 years on hold"