Test the cable. Wear the headphones and turn on audio. Bend the cable 90 degrees across the top of your thumb and run it along the length of the cable. When the sound crackles or cuts in and out, you have found the problem. If the problem is near the plug, see Fixing the Plug for repair instructions. Otherwise, continue to the next step.
When you know that you've found the site of the break, mark it with a piece of electrical tape.
If you already found the problem with a multimeter, skip this step.