3-Way Switch: Light-Switch-Switch
Three-way switches are not too much more complicated than the average switch, but they do take a certain amount of care and study. The first time I ever wired one, I started a brief fire in one of the switch boxes. For this reason it is wise to follow instructions closely. If you are unsure of what you are doing, it might be best to consult a qualified electrician.
In the diagram at left the light comes first and the switches follow. This is a very common occurance when changing a light over from a regular switch to a three-way switch. So we see the source of the power comes into the light's box. But it must go to the switches before it can go to the light. This is why the black wire, which is bringing the current in does not get connected directly to the light. It is carried first to the switches through a white wire marked black.
When white wires are used to carry current they are commonly marked black, either with a marker or by wrapping them partly with a piece of electrical tape. There is a special wire called "three wire cable with ground" that will be necessary in all the different configurations of a three-way switch circuit. This extra wire allows the three way switches to carry current through a variety of paths. In our diagram on this page the red wire is placed between the upper connection on each switch. This will NOT be the case for every cofiguration of this type of circuit.
The ground connection in these diagrams presupposes the use of metal boxes. If you are using plastic, the grounds will not be connected to the boxes via a screw.