writes:
On Tue, 24 Sep 2019 18:38:47 GMT, (Scott Lurndal)
wrote:

You get around the party line thing by connecting the green and yellow
together.

That's not precisely correct. You remove the shell of the phone and
move a connection on the terminal block from one terminal to another.

The yellow and black wires (on the modern POTS side) are N/C.

Red and Green (Ring and Tip) are the only wires connected.

https://www.beatriceco.com/bti/porti...hones-500.html

Scroll down to "do you have a model that doesn't ring".

A rotary dial phone would have had a 3 wire line set, red, green and
yellow.

Nonsense. I've three WE500 and one WE300 desksets. None of them
had three wire for the POTS service. POTS service has always been two wire (tip and ring);
the yellow and black wires were used for lighted dials (with a transformer
on premises) on certain model phones. In some installations, the yellow
was tied to local ground.

Look at the Bell wiring diagram noted above.