DIY Guide to Installing a Telephone Jack

This home wiring job is easy to do on your own, without paying for a contractor

Two telephone ports on a wall with one disconnected

 Adri Berger / Getty Images 

Phone-jack installation is one of the few basic wiring jobs most homeowners can do. Home automation applications may include installing phone extensions in additional rooms or installing a second phone line in the house.

Automation enthusiasts continually look for ways to make their homes more convenient, and installing additional phones is one of the ways they do it.

Before getting started, map out where in the house the phone jack should be. Consider where any desks or tables might sit so that you can avoid having wires stretched to their limits or hanging between desks.

Types of Home Telephone Wiring

Phone plug and jack
Wikimedia Commons

Telephone cable typically comes in the four-strand wire, although six-strand wire and eight-strand wire are not uncommon. The various strand types are referred to as two-pair, three-pair, and four-pair.

A conventional four-strand telephone cable normally uses four colored wires in red, green, black, and yellow. These colors are the industry standard.

Although most telephones use four or six contact connectors, standard telephones only use two of the wires. Single-line telephones are designed to use the two center contacts in the phone connector.

On a four-contact connector, the outside two contacts are not used and on a six-contact connector, the outside four contacts are not used. This architecture is important to know when wiring the phone jack.

Installing Single or First Phone Lines

Whether you are installing a modular surface mount or flush mount jack, the wiring is the same:

  1. Remove the front cover. The inside of the connector is wired to four terminal screws. The wires should be red, green, black, and yellow.

  2. Connect your hot phone wires (red and green) to the terminals with the red and green wires.

Although red and green are commonly used for hot phone lines, older or improperly wired homes could have other colors in use. To ensure you’ve got the right wires, use a phone line tester to check that the wires are hot. Another easy way to check the wires is to hook them up to the terminals, plug a phone in to the check and listen for a dial tone.

Installing Second Phone Lines

Most homes are wired for two phone lines even if only one line is in use. It’s common when ordering a second phone line for the phone company to activate the second line remotely without ever coming to your home. When they do this, they are turning on your second pair (the black and yellow wires).

The outside contacts in a single-line phone connector aren’t used. Two-line phones often make use of this outside contact pair so that no extra wiring is required (providing you have the black and yellow wires connected inside the jack).

If you plan to use a single-line telephone for your second line then you must install a modified phone jack:.

  1. Remove the front cover of the phone jack and connect your yellow and black wires to the red and green terminals. This step will cross your second phone line to the center connector contacts so you can use a standard single-line phone.

  2. If you experience problems, use a phone line tester to ensure the new second line is active.