We have probably all had this happen to us at some point. You buy a decent pair of headphones, but after a few months, they break. The failure mode of these devices is typically (at least in my experience) the wires connecting to the speaker inside the headphones, or the wires connecting to the 3.5 mm jack. Interestingly enough, headphones are incredibly simple devices, and these failure modes are easy to correct. The headphone jack has three (or four) terminals (the 4th terminal can be for a microphone or for volume control as with Apple earbuds). The two outermost (away from the wire) terminals are the signal line, for the left and right sides respectively. The terminal closest to the base is ground. Inside the earphones is a speaker.

Each speaker has two terminals: signal and ground (or common). The wiring is simple. The ground terminal on the headphone jack connects to ground on both speakers, while the two signal terminals (for left and right) go to the left and right speakers respectively. It does not appear to matter which signal line you connect to the left or right speakers. It appears to work either way. There is probably some manufacturing standard, but I do not know what that is and you do not need to know that for this to work.

I bought my little sister these headphones a while back and they broke in a year or so. In response, I am fixing them for her. In this Instructable, I will demonstrate to you how to rewire a pair of broken headphones.

Step 1: Gather Up Your Tools

1 x soldering station (iron, solder, flux, helping hand, whatever you need)
1 x broken headphones
1 x replacement 3.5 mm jack
some jumper wire - I recommend 28 AWG or smaller

Step 2: Determine Your Failure Mode

You should figure out what part of your headphones is actually faulty. You can do this a few different ways, of course. However, this is how I did it.

I took a male-male 3.5 mm jack. This means the jack is on both sides. So something like this.
I connected some alligator clips to one of the signal terminals and to the ground terminal.
I plugged the other end of the jack into my iPhone
I connected the other end of my alligator clips to the speakers of the headphones.
Played a song.
If I heard sounds out of the speakers, that meant the speakers work and the failure is somewhere along the wire
Result: speakers work
Next action: Replace the wire

If your speakers do not work, then your speakers are probably broken and need to be replaced.

Step 3: Remove Outer Casing

This is pretty obvious. In order to get to any of the wiring, you need to remove the outer portion of the headphones to expose the connections. These Hello Kitty headphones came apart really easily.

Step 4: Desolder the Current Connections

When you take a look at the speaker, you can see the wires connecting to the two terminals. I don't think that there is a specific "ground" on the speakers. I think it can go either way. Again, there is probably some manufacturing standard that I am not aware of. I noticed that one of the speaker terminals was colored green and the other was colored red. This was consistent for both speakers. I chose to designate the green as ground because green typically denotes earth ground.

Step 5: Solder Your Replacement Wire

Again, pretty self explanatory. Cut yourself a good length of wire and solder it to the terminals on the speakers.

Step 6: Solder Your Wire to the Replacement 3.5 Mm Jack

Solder the two ground wires to the ground terminal of the 3.5 mm jack and the two signals wires to the signal terminals.

Step 7: Add a Little Bit of Tape to Keep Your Wire Together

I used a bit of tape, about an inch long, and taped the wire together so they do not get tangled. The bits of tape were spaced about 6 inches apart from each other.