Most of you have encountered a time when you spent half the day decorating for Christmas and then start to plug in the Christmas tree or other decorations and instead of gasps of delight discover that part of your lights are not working. There are many different reasons why a string of Christmas lights does not work properly. It is easy to troubleshoot and remedy the problem, but it takes persistence and patience.
Check the entire strand of lights for a missing, damaged, or abnormal looking bulb, according to the Christmas Light Company website. You may find that the bulb has a black or silver-looking stain on the inside. If this is your problem, carefully replace the bulb after first unplugging the string of lights.
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Using your fingernail or a pencil, flick each light bulb carefully while the strand is still plugged in. If it flickers and goes out again, the problem is a loose bulb. Tighten the bulb gently and checked to see if the rest of the strand lit up. If the bulb does not come on after tightening it, remove the bulb and check to see if the center wire is in the middle of the bulb, if it is not, discard the bulb and replace it with a replacement bulb.
Remove the first bulb that is not working in the half strain of lights. Take the bulb you just removed and replace it, then remove the second bulb in the string and repeat this process until you have taken out each bulb and replaced it with another bulb in the entire strand of lights. Each socket must contain a bulb in order for the strand of lights to work. This will help you discover which bulb is the culprit.
Purchase a light bulb tester, you can find this at discount stores that sell Christmas lights or hardware stores.