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How to Find the Bad Bulb on a String of Christmas Lights

(14 votes, average 4.21 out of 5)
Written by Cindy M   

find the bad bulb on christmas lights

Intro: One bad light bulb can ruin the entire string of Christmas lights and it seems impossible to figure out which bulb is bad. Follow these steps to eliminate the bad bulb and get your Christmas lights up and running again.


Step 1: Skim through all of the bulbs. The bad bulb may have burnt out and left some black residue on the inside of the bulb. If you find that burned out bulb then switch it out for a working bulb and see if the string works. If it doesn’t work then we have the wrong bulb. If they all the bulbs look fine then consider yourself unlucky and move on to the next step.


Step 2: Purchase a hum-tracing device which is usually only a couple of dollars found in the hardware section. There are three wires on a string of Christmas lights, one which is hot, one is neutral, and one that travels from light socket to light socket. When using the hum tracer, you should only be testing the wire that goes between the sockets.


How to Find the Bad Bulb on a String of Christmas LightsStep 3: Plug in the Christmas lights and turn on the hum tracer. Use your hum tracer and test the wire going to and leaving each bulb. If the hum tracer hums then there is 120 volts traveling within that wire. If the wire going to and leaving the bulb both hums then that bulb is fine. Do this for each bulb until you find the dead bulb and then replace it.


Step 4: If you don’t have a hum tracer or do not want to get one then you’ll have to pull out each bulb one at a time and put in a new one until you find the burnt out bulb. If there is more than one burned out then this method is not really going to work for you.


Tips: You can save money in the long run by buying a hum tracer.


Warnings: When replacing bulbs, make sure the Christmas Lights are unplugged.

Comments (5)add comment

Donna Thacker said:

Donna Thacker
Finding bad lights drives me crazy! I'll have to get one of these hum thingys!
September 19, 2009
Votes: +1

paul said:

It seems that every year there is always one bulb which messes up the entire string of lights!
November 30, 2009
Votes: +1

Carl Benjamin said:

Carl Benjamin
Very helpful this time of the year.
December 01, 2009
Votes: +1

jmarwayne said:

Looking for the bad bulb is a holiday tradition!
December 03, 2010
Votes: +2

Christina Fernando said:

Christina Fernando
I always hate it when that happens. Thanks for the tips!
December 04, 2010
Votes: +1

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