Modern telephone cords have been in use for a long time, with little change since their invention in the 1970s. Finding phone cords in the store can be tricky today; many stores have stopped carrying telephone cables since so many people only use cell phones now. This rings especially true for coiled handset cords. With these cables becoming rarer, sometimes it is better to repair rather than replace them. Other times, users may just need a cable not available in a standard length.

There is a bit of variation with different connectors available, as well as different wiring schemes (called pinouts) for the smaller wires inside the main cord. This guide will cover how to attach a connector to the end of bare phone cable and the difference between wiring pinouts.

Step 1: Gathering the Supplies

There are a few simple supplies that will be needed for an installation or repair. The key components are the bare phone cable and the correct type of connectors. There are three main types of connectors that can be used. RJ12 is the most common, being used on flat line cords that connect the base of a telephone to the wall. RJ11 is an older version of RJ12, and they are the same size. The difference is that RJ11 uses four internal wires (called conductors) while RJ12 uses six. RJ12 is backwards compatible with RJ11, but RJ11 will not work with RJ12.

Coiled handset cords use a smaller connector called RJ9 or RJ22 (both names refer to the same thing). These are physically smaller than RJ11/RJ12 and use four conductors.

Beyond the connectors, just a few tools are needed. A modular crimper is essential in any scenario. A pair of small scissors will also be handy for trimming away any excess wire. Testers can also be useful once a cable is assembled/repaired to make sure it works correctly. Testers are also great for pinpointing the exact problem with a damaged cable, such as identifying a specific wire inside the cable that is faulty.

Crimp tool Crimper RJ11 RJ12 Flat cable Phone

Step 2: Stripping the Jacket

Most crimp tools used for telephone cables are equipped with a blade for stripping the jacket. Otherwise, you will want to use a pair of scissors to carefully remove the jacket. If using scissors, be sure not to damage the conductors (if the conductors do get damaged, cut them off and start over). The exposed wire should be roughly the same length as the connector they will go into.

Jacket RJ12 RJ11 Crimp Tool Crimper

Step 3: Attaching the Connector

Insert the connector over the now exposed conductors, with each wire lining up with one of the metal pins (called contacts) inside the connector. There are two different ways flat line cords can be wired, straight and reverse. Straight cables have the colored wires in the same order on both sides of the cable. Straight pinouts are used for data signals, like a fax machine. Reverse cables have the colors in one order on side A and in the opposite order on side B. Reverse pinouts are used for voice signals, like a telephone.

Phone cord cable straight reverse pinout wiring scheme diagram

A straight pinout (left) vs. a reverse pinout (right)

Make sure the conductors are touching the contacts. If they are not touching or barely touching, the signal will not travel all the way through the cable and it will not work. In this scenario, the existing connector must be cut off (they cannot be reused) and replaced with a new unit.

Phone RJ12 RJ11 Straight Reverse Pinout Wiring Scheme

Step 4: Crimping the Connector

Insert the connector into the crimp tool and squeeze tightly to ensure the connector is firmly attached to the cable.

Crimper Crimp Tool RJ11 RJ12

(Optional) Step 5: Testing the Cable

Insert the phone cable into the tester and press the start button to begin the test. If all the lights turn green, the cable is fully functional. If one or more lights turn red, that specific conductor is not making a connection. In the event the cable fails, one of two main issues could be occurring. The first is that the failing conductor is not touching the contact. This can also happen if they are not touching enough, making the signal too weak to work. If that happens, cut off the connector and try again.

The other potential issue is damage to the cable. If a cable has a kink in it or was bent too much, the conductors can be damaged and become unusable. The damage may be visible from the outside, in which case the damaged part of the cable must be cut off. If doing this would make the cable too short or if the damaged spot cannot be located, the cable will have to be replaced instead.

Phone RJ11 RJ12

Video Guide:

*Note: In the guide below, EZ-RJ12/RJ11 jacks are used. These jacks allow any extra wire to go through the end of the connector and be trimmed off after the connector is attached. Conventional RJ12 and RJ11 connectors do not do this. The length of the wires will need to be equal (or very close to equal) to the length of the connector prior to installation when using regular connectors.