RJ-11, RJ-14, and RJ-25 Modular Jack Wiring Apr 16, 2018RJ-11, RJ-14, and RJ-25 Modular Jack Wiring If your visit to the Classic Rotary Phones Forum was enjoyable or helpful, you may tell us by making a small donation. *RJ25 is the interface for three telephone lines. It uses all six pins of a 6P6C connector. The pin assignments and standard color designations for these, the most commonly used Registered jack - Wikipedia The most widely implemented registered jack in telecommunications is the RJ11. This is a modular connector wired for one telephone line, using the center two contacts of six available positions, and is used for single-line telephones in homes and offices in most countries.