The wiring principles for headphone jacks are the same, whatever size jack is used. They have three terminal connectors; one is the right audio, the second is the left audio and the third is the common ground terminal. A 3.5mm headphone jack is typically used to connect your headphones to a music player or iPod. You may find that the wires disconnect from the terminals, in which case you need to fix the jack. While rewiring is moderately easy, the main issue with a 3.5mm headphone jack is the size, as it's very small and difficult to manipulate.
Remove the plastic cover from the 3.5mm headphone jack. Hold the metal jack pin using one hand and then screw the cover counter-clockwise using your other hand until it comes away from the metal pin. Slide the cover a few inches up the wire so it's out of the way.
Cut the wire about an inch from the end where it connects to the headphone jack using a knife. It's best to completely rewire so you fix it properly.
Strip off ½ inch of protective plastic from the end you have just cut using wire strippers. Do this carefully as the internal wires are very thin. Three coloured wires are exposed -- usually red, black and white -- but the colours can vary.
Use the wire strippers and remove about one 1/8 inch of coloured plastic. Take care, as the wire strippers can easily cut though the wires, meaning you need to start over.
Look on the jack plug to see how the existing coloured wires connect to the terminals on the jack plug. Use a pen to write down the colour of each wire that goes to each terminal, so you ensure you rewire it the same. If you have one loose wire but two are connected, then it's obvious where the loose wire needs to get connected. However, if more than wire is disconnected, you need to look closely at the terminals on the jack plug. They are marked "+" or "R" for right audio and "-" or "L" for left. The other terminal is usually labelled "T" for common ground.
Heat a thin-tipped soldering iron. Touch the terminals briefly using the tip of the soldering iron so it heats up and melts the existing solder. Remove the tip of the soldering iron from the terminals and immediately remove any wires that are attached to the terminals using your fingers.
Touch the end of the soldering iron onto one of the exposed wires that go to your headphones. Introduce a little solder and let it melt and coat the wire. Repeat the process for the other wires so they are all coated in solder.
Refer to the note you made earlier so you know which wire goes to each terminal. Alternatively look on the jack plug for symbols. Place the red wire onto the terminal labelled "+" or "R" and then touch the wire using the end of the soldering iron so the solder melts. Remove the soldering iron immediately, but hold the wire in place until the solder hardens. Repeat by attaching the black wire to the "-" or "L" terminal and the third wire to the "T" terminal, using the soldering iron.
Turn off the soldering iron. Slide the jack plug cover down the wire and then screw the cover onto the metal jack plug using your fingers.