Christmas light wiring is fairly simple and straightforward. The bulbs are set up in a series with each bulb connected to the next. The main wire comes from the plug that is connected to the wall. It is run to the first bulb in the line and attached to one side of it. Wire is then attached to the other side of the bulb and run out to the next bulb in the line. This continues until all of the Christmas lights are connected together. The wire is then run back to the plug to complete the circuit. Most strings of lights also have the ability to add extra strings to make the lights longer. To do this, more wire is connected to the end of a series of lights in order to attach another plug to the other end. The plug on the second end does not have tongs, but instead is designed like an outlet so that the next string of lights can be inserted into it.
There are two wires that come up into the bulb. These wires come out of the bulb and bend to the sides of the bottom. The bulb is inserted into a slot where the outer wires connect to the main wires as they run up into the same slot. Inside the bulb, the two wires are connected together by a filament. When power is supplied to the line of Christmas lights, the filament will brighten.
Keeping the String Lit
In the old days, when one bulb in a string of lights burned out, the whole string would go out. The only way to light them up again would be to painstakingly check each bulb until the one that was bad was found and replaced. These types of lights are not as popular today but can still be found. The more popular lights do not go out when one bulb is damaged. This is accomplished with a shunt. The shunt is connected to the two internal wires below the filament. This way, when the filament goes, the wires stay connected and the circuit is not broken.