How to Wire a Telephone Jack

Telephone jack's exposed wires held by hand

The Spruce / Kevin Norris

Project Overview
  • Working Time: 15 - 30 mins
  • Total Time: 15 - 30 mins
  • Skill Level: Beginner
  • Estimated Cost: $5 to $10

Modern wireless telephone systems have largely eliminated the need to outfit your home with many phone jacks, since a central phone jack can now serve a single transmitter/message unit that sends signals to several wireless remote handsets that can be used anywhere in the house. And there are now many homes that have no land-line phones at all, relying instead on cell phones only. At one time, it was common for homes to have a phone jack in every room; today's homes may have none at all.

But if your home still has a landline, it's sometimes necessary to establish additional phone jacks that are hard-wired to the main telephone system. For example, in very large homes, wireless receivers may have trouble receiving the signals from a single transmitter. In these instances, the solution is often to run phone cables to remote locations and install jacks that can serve their own transmitters. It's also possible you may need to replace the main phone jack that serves the central cordless transmitter, should it wear out.

Fortunately, this increasingly rare DIY project is still quite an easy one to complete.

Before You Begin

In older telephone installations, the phone cable typically has four small-gauge wires inside the outer jacket: red, green, black, and yellow. If you're extending a line to a room or other part of the house, you can continue to use this type of cable, or you can use newer Category 3 or 5 (Cat-3 or Cat-5) data cable, which also has multiple wires but with a different color scheme. Cat-3 or Cat-5 cable works just as well as the old cable for phone service, and it works much better for data (such as for a DSL internet connection). With either type of cable, once the cable is run to the jack location, the wiring of the jack is a simple matter of matching up the correct wire colors.

Our project assumes the phone cable to the new jack location has already been installed. Running phone cable is generally any easy process, in which the wires at one end of the cable are first attached to the matching screw terminals on the main phone terminal block. After the cable is run through the walls or under the floor to the new location, finishing the job is usually just a matter of hooking up the wires to a new jack using the same color-coding. Running phone cable through finished walls uses many of the same techniques that are used for running electrical circuit cable, but the job is considerably easier since phone cable is quite small and flexible.

Safety Considerations

Telephone wires inside your home carry a very low-voltage electrical current and are generally quite safe to work on without shutting off the power. In fact, only the phone company can shut off the power to the phone system. But just to be safe, don't work on phone wiring with wet hands or when standing in water.

What You'll Need

Equipment / Tools

  • Wire strippers
  • Screwdrivers
  • Needle-nose pliers

Materials

  • Telephone jack
  • Wood screws or drywall screws

Instructions

Materials and tools to wire a telephone jack

The Spruce / Kevin Norris

  1. Strip the Outer Sheathing

    Strip 2 to 3 inches of the outer sheathing from the phone cable, using wire strippers. An old-style four-wire cable can be stripped using the 10-gauge slot on the wire strippers. Rotate the strippers as needed to cut all the way around the sheathing, being careful not to cut into the insulated wires inside the cable. Pull the cut piece of sheathing off of the end of the cable to expose the inner wires. 

    Alternatively, some phone cables have a pull cord inside that strips the sheathing as you pull back on it. In this case, start by stripping only a small amount of the sheathing using wire strippers, then use the pull cord to cut back the sheathing 2 to 3 inches. Trim off the portion of cut sheathing, using the cutters on the strippers or using cutting pliers.

    Wire strippers stripping the outer sheathing of phone cable

    The Spruce / Kevin Norris

  2. Untwist and Strip the Individual Wires

    Untwist the individual wires inside the cable from one another. Strip 1/2 to 3/4 inch of insulation from each wire that you need, using the 20- or 22-gauge slot on the wire strippers. In many cases, you'll need to strip only two of the wires if you are installing a standard one-line residential phone line. A second pair of wires is used if you are installing a second line, such as a second voice-phone line. 

    Then, identify the individual wires you'll be using:

    Old four-wire cable:

    • Line 1 (primary phone line): red and green
    • Line 2 (secondary line): black and yellow

    Cat-3 or Cat-5 cable: 

    • Line 1 (primary phone line): blue and white-with-blue-stripe 
    • Line 2 (secondary line): orange and white-with-orange-stripe
    Individual wires untwisted and insulation stripped with wire strippers

    The Spruce / Kevin Norris

  3. Install the Mounting Plate

    Remove the cover from the front of the phone jack, exposing the mounting plate and mounting screw holes. If the phone cable has been run inside the wall, thread it through the opening in the plate as you position the plate against the wall over the access hole. If the phone cable is surface-mounted, such as onto the front of a baseboard, the cable typically is inserted through a notch in the side of the phone jack. 

    Mount the plate to the wall, molding, or other structure, using a screwdriver and small wood screws or drywall screws. Some phone jacks may have self-adhesive strips for securing the plate to the wall, but if this type of jack also has screw openings, it is a good idea to reinforce the installation with screws. 

    Mounting plate secured to wall with screwdriver

    The Spruce / Kevin Norris

  4. Connect the Wires

    Connect the stripped wires from the phone cable to the corresponding screw terminals on the jack, using the following color combinations (each jack terminal is identified by the color of the wire that is preattached to it):

    Old four-wire cable: 

    • Line 1 (primary phone line): red wire to red terminal; green wire to green terminal
    • Line 2 (secondary line): black wire to black terminal; yellow wire to yellow terminal

    Cat-3 or Cat-5 cable: 

    • Line 1 (primary phone line): blue wire to red terminal; white-with-blue-stripe wire to green terminal
    • Line 2 (secondary line): orange wire to yellow terminal; white-with-orange-stripe wire to black terminal 

    To make the wire connections, loosen each terminal screw with a screwdriver. Wrap the bare copper end of the wire around the screw in a clockwise direction, using needle-nose pliers. Tighten the screw to secure the wire. The wire insulation should just touch the screw terminal and there should be no excess bare wire extending out from the screw.

    Stripped wires connected to screw terminals with screw driver

    The Spruce / Kevin Norris

  5. Reinstall the Cover

    Reinstall the cover onto the jack's mounting plate. Some covers are secured with a screw; others simply snap into place. Plug a phone into the jack to make sure the line is working properly. 

    Phone jack cover reinstalled by snapping into place

    The Spruce / Kevin Norris