Phone wires always come in pairs. The only two you need are the green/red
pair. The other pair in 'normal' houshold phone wiring is yellow/black.
Yellow/black has been used for a number of things over the years, the most
notable being the use to provide power on *some* early lighted dial phones,
mostly in the independent telephone comapny territories (GTE especially).
Today, yellow/black is typically the second phone line.
For historical purposes, the two wires in an active phone line are
called 'tip' and 'ring'. Not, as you would expect, standing for ring as
in bell, but ring as in the circular part of a connector that looks alot
like a 1/4" headphone jack. Once you understand the ring morphhology, the tip
part is pretty obvious. This all derives from the plugs used in early, human
operated telephone 'plugboards' or switches.
Telephones work on a system of -48Vdc. In the early days of touchtone,
the touchtone phones were sensitive to polarity, and would not work
it tip/ring were swapped. This is, unless you are trying to use
an old Western Electric touchtone phone, no longer generally the case. Most
phones cope with swapped tip/ring quite well. Most of the modern lighted dial
phones pull their power from the tip/ring pair.
green - ring
red - tip
black - ring2
yellow - tip2
While the wires coming into the house may appear black, take another
look at them. They are usually a black jacket over a green or red inner liner.
But that's probably more than ya'll really wanted to know.
Bob
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