We can use broken earphone cables for many DIY home projects. In this instruction I explain to my 6 years old son how to find corresponding ends of wires in the cable using simple flashlight as a tester.
There are three wires on one side of the cable: yellow, white and red. And there is a male audio connector on the other side of the cable. We have to clean up about 3 cm of insulation from each wire. You can remove the insulation from wires using special tools (knives, wire cutters or even open fire.) Always follow basic safety rules! Each wire is made of many thin wires. You have to roll them together. The male audio connector has three parts: tip, ring and ground. We have to find out which wire is connected to each part of the male connector. We can do it with a multimeter tester. In this example I am going to use a flash light as a tester. I salvaged this flash light from used lighter. Surprisingly the flashlight works as a new one!
We can use any simple flashlight as a tester. Or we can make one from LED and batteries.
Interesting fact about LED. Led allows electrical currant flow in one direction only! If we connect LED to a battery in right way then the LED will emit light. Otherwise there is no light. You can find more about LED at: http://electronics.howstuffworks.com/led.htm
The LED of this flashlight is already correctly attached to the batteries. Let's separate the on/off switch. I am going to test one wire at a time. Connect or hold one wire to the switch at the LED side.
Use the long end of the switch to touch parts of the male connector. The LED will emit light only when you touch the connected part of the male connector. Write down the result. Then check the other wires in the same way.
In this example the yellow wire corresponds with the ring. The white wire corresponds with the ground. The red wire corresponds with the tip. Now we can use this audio cable for DIY home projects. Have fun and happy testing :)