Why does analog phone cable have 6 copper wires when it only uses one pair of them??
Phone wires up through about 1970 consisted of four wires– red and green for the main phone line, and yellow and black as a spare line. Then when the trimline and princess phones came out they used the yellow and black to supply power for the dial light. But then there was no spare line available, so when they designed the RJ-11 they added a third pair.
