BG>>  Yellow is ground and black is for AC.. Explanation:  When the princess
 DG>> This may have been true at one point.  These days, however,
 DG>> the codes are:
 DG>> Cable       Pair         Tip        Ring(Ground)
 DG>> ----------- ----         -----      ------------
 DG>> 2 pairs       1          Green        Red
 DG>> 2          Black        Yellow
 BG>  The above is for 4 wire house wiring to jacks, he asked what it was
 BG>  used for.  Originally wiring was only 3 wire with tip/ring/ground. It
 BG>  wasn't until the princess phone and its little light bulbs that the
 BG>  black wire was added to carry the on premise transformers ac to power
It probably varies in some areas because 4 wire house wiring was already in 
use before the princess phones, the wiring in this house was done in 1958, as 
far as I can remember that's before the princess phones, and it's all 4 wire, 
read and green, yellow and black. After all, this is Jersey, and RED is tip 
here, not green.
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