Determining if a wire has power is useful in repairing home and automobile electrical systems. It is also beneficial for creating a safe working environment around electricity. When fixing or modifying electrical systems, it is important to have the power supply shut off to the wires you are working on. It only takes a very small amount of amps to stop the human heart; a few minutes of work can protect you against the dangers.
Connect the test light's alligator clip to the bare ground wire. In automotive applications, black wires are typically the ground wires. You can also use any area of bare metal on a car. For residential applications, the white wire is typically the ground.
Touch the bare wire you wish to check for electricity with the test light's probe.
Look to see if the test light illuminates. If it does, there is electricity in the wire.
Turn the power on to the non-contact voltage tester with the button on its top. Voltage testers will normally make an audible sound or flash their lights to indicate it is on. If it doesn't, replace the battery and try again.
Bring the tip of the voltage tester close to the wire you wish to check for power. The non-contact tester detects the electrical field around live wires.
Look to see if the test light illuminates. If it does, the wire has electricity.
The preferred method to test a wire is with the non-contact detector. They are safer because they don't require you to touch the wire prior to finding out if it has power.
Working around electricity is inherently dangerous. Take the necessary precautions to protect yourself.