I have a SC turret switchboard that I have been workin on.
Posted earlier, look it up yourself.
It was incomplete, that it did not have the Relay cabinet with it.
The cabinet holds the relays for the lites, Hold, and some other stuff.
Since no one has any info on them, I made my own. DSK can appreciate this.
It currently lites the White lite when the station is taken off hook.
And when the OP places the Line Key for that extension in Listen mode, the white goes out, and the Busy Red lite lites.
They go out when the station hangs up. I don't have any info on the way the HOLD portion works, but this will be
used to connect 1 or 2 extensions to my pots line, and/or my switchboard, so it is good enuf for what I need.