How to Replace a Bulb on a String of Christmas Lights

Most all Americans love Christmas lights. Even people who dislike shopping seem to love the spirit of Christmas, decorating, and Christmas lights. But what most of us do not like is finding Christmas light strings that don't work. Usually it is because of a single defective bulb. We discard many otherwise good light strings because we don't know how to find and change the bulb that ruins the entire string. If you would like to know how to find and change one of these defective light bulbs, just follow the 4 steps below.

Things You'll Need:

  • Hum-tracing device

Step 1 – Locate Dark Bulbs

Finding the defective bulb in a string of Christmas tree lights is almost always the greatest challenge you'll have. It is not easy to identify the offending bulb. When a single bulb becomes defective it can extinguish all lights on the string. Some burned out bulbs become darker than the good bulbs, and occasionally you can identify the bad bulb as one that is darker, then replace it with a good bulb. But not always.

Step 2 – Locate Built-In Shunt Bulbs

Some of the newer light strings are made with a built-in shunt. In these strings one bulb can become defective without making all other bulbs stop working. If all bulbs on your light string are working except for one, it is likely that this string has the shunt feature built into the string. In this case, you can easily identify the bad bulb as the only one that is not lighted. Then, you can easily replace it by simply pulling it out of its socket.

Step 3 - Use a Hum Tracer

Use a hum tracer to find a defective bulb. If your light string includes three strands—or wires—you should first identify which of the three strands (Strand A) runs from bulb to bulb. Strands B and C do not connect to each bulb. Because all three strands are usually twisted together it is sometimes difficult to tell which of them is Strand A. You may need to spread them apart to find the right strand. Once you've identified Strand A, touch it with the tip of your hum tracer. If you hear an electronic hum, this means there is an electric current flowing through this strand. It is usually at a defective bulb that this current stops flowing. If you can locate a bulb where you get a hum on the incoming strand but not on the outgoing strand, this is an indication that the bulb you tested is defective.

Step 4 – Replace a Bad Bulb

Once you have identified a bulb as one that is probably bad, you can replace it with a new one. If the string lights come on, you have solved your problem. If the new light fails to come on, there are 3 possible reasons: 1) there is at least one other light on the string that is bad, 2) Strand A wire may be severed or shorted, or 3) the new light bulb may be bad. If you cannot find another bad light bulb, you will likely need to replace your light string.