In older homes, you may find a whole different scheme, called "quad" wiring, which contains four wires colored red, green, yellow, and black. The primary phone line is normally the red and green wires. Sometimes you will find a second line on the yellow and black wires, but this is not good practice because, in quad cable, the wire pairs are not twisted together, which can result in "crosstalk" between the two lines. That is the main reason why "quad" wire is rarely seen in homes newer than a decade or so (in fact, it is a violation of a Federal Communications Commission rule to use any wiring that does not meet at least Cat 3 specifications for new and retrofit telephone wire installations made aft