Stereo phone jacks are available in different sizes. The original phone jack, referred to as the 1/4-inch (6.5mm) phone jack, dates back to around 1878. It was used in telephone exchanges and is still available today. Phone jacks are now much smaller but do the same job. The 1/8-inch (2.5mm) phone jack is mainly for use with cell phones while the slightly larger 3/32-inch (3.5mm) phone jack is used to connect headsets to iPods and MP3 players.
Stereo phone jacks consist of a central pin with three insulated sections enabling the sound it carries to be split into right and left speakers (or earpieces) producing stereo sound. Wiring the smaller type of stereo phone jacks can be intricate, but the task is fairly straightforward.
Strip 1/2 inch off the outer plastic coating of your stereo cable using a small knife or wire strippers. There are four wires inside. Two are covered in coloured plastic (usually red and black) and two are bear wires.
Twist the two bear wires together leaving you with three wires. These will attach to the three terminal in your stereo phone jack.
Strip 1/4 inch from the two coloured wires with a small knife or wire strippers. You need to do this very carefully if you are wiring a small phone jack. If you cut through either wire, start over.
Use your soldering iron and gently touch the top of the twisted wire. Introduce your solder and as soon as it melts remove the soldering iron and solder. The melted solder will coat the wire and harden in seconds.
Repeat the process on the two remaining coloured wires. Ensure you don't touch the plastic with your soldering iron as you will melt the plastic and have to start over.
Unscew or pull the cover from your stereo jack, depending on the type. Slide the wire through the stereo phone jack cover ensuring the end that attaches to the phone jack faces the end of the wire.
Check the phone jack to see the method of fixing the wires to the jack. There are two ways: it will either have three small screws that loosen, then your wire slides under before tightening, or there are three thin metal pins. If the phone jack has pins, your wires need to be soldered to the pins.
Use your soldering iron to attach the wires to the pins, or unscrew the three screws enough to be able to insert the wires. Don't unscrew too far as they will detach from the phone jack and you will have difficulty finding them. If you have a small clamp, place the phone jack in it so it's held steady.
Touch your soldering iron to the central pin. The pin is longer than the other two and may be marked "ground." Place the twisted bear wire on the pin and let the solder on the wire melt so it covers the pin and fuses together. Remove the soldering iron and allow the phone jack and wire to cool completely. If your phone jack has screws, insert the bear twisted wire under the screw and tighten.
Place the red wire on the pin marked "R" or "+" if it is labelled. If not, then select either of the remaining smaller pins as it doesn't matter which is used. Touch your soldering iron on the pin and wire until the solder melts. If your phone jack has screws, insert the red wire under either screw and tighten gently. Use the screw marked "R" or "+" if it's labelled. Repeat the process for the black wire, attaching to the remaining pin or screw.
Check the three wires are fastened neatly and none are touching another. Slide the cover down the stereo cable and screw or push the cover over the phone jack. Plug your phone jack into your stereo equipment to check it functions properly.
Some stereo cables have four coloured wires instead of two coloured and two bear. If this is the case, use the red and black for your right and left pins. Strip 1/4 inch off the remaining two coloured wires, then twist together and use these to connect to the central pin or screw.