A light and a switch is one of the simplest electrical circuits that demonstrate how electricity works. 120 volt electricity is provided through three wires. The black wire, which is the "hot" wire, delivers the electricity from the distribution panel to the light. The white "neutral" wire provides the path for the electricity back to the source. The bare or green wire is the ground wire for the circuit. This is the safety system and provides a path for the electricity to make it back to the ground in the event it gets somewhere it shouldn't.
Things You'll Need
Non-contact voltage tester
Twist on wire connectors
Turn off the power to the circuit you are working on at the electrical distribution panel. This is done by tripping the breaker or removing the fuse at the panel.
Confirm there is no electricity at the wires for the switch and light with a non-contact voltage tester. Turn the tester on by pressing the button on its side. The tester should illuminate or make an audible sound as confirmation it is working. Touch the tip of the tester to the black, white and ground wires. If the tester illuminates or beeps there is still power at the wires.
Strip 1/2 inch of insulation off two black and two white wires at the electrical box for the switch.
Connect the two black wires to the two terminals on one side of the switch. The connections are made by backing off the terminal screw with a screwdriver, wrapping the end of the black wire around the screw in a 3/4 circle, then tightening the screw back down.
Connect the two white wires together by twisting the two ends of the wire together with pliers. Then install a twist on wire connector on top by twisting it on. There should be no bare wire exposed at the bottom of the connector.
Cut a five-inch section of bare metal wire from one of the ground wires. Fasten this wire to the grounding screw on the inside of the electrical box in the same method you connected the black wires to the switch.
Connect the source side ground wire, the light ground wire and the box ground in the same method as you fastened the white wires.
Connect the ground wire to the electrical box for the light in the same method as you connected it to the switch box.
Fasten the black wire to the "hot" terminal on the back of the light in the same method as you fastened the black wires to the switch.
Fasten the white wire to the "neutral" terminal on the back of the light in the same method as you fastened the black wire.
For a 120 volt, 15 amp circuit, 14 gauge copper wire is the standard size.
Working with electricity is dangerous because you can't see it and it can kill you. Do not attempt this project unless you understand safe electrical practices.