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Troubleshooting Christmas Mini-Light Strings Answered

I searched Instructables to be certain I am not covering something someone else has already done, but found nothing. 

Here is an excellent article on troubleshooting a bad string of Christmas mini-lights. (I do not know the author and am not connected to him in any way.) 

I know of three occurrences of non-working light strings from this year's celebrations. In the first case, the woman who owns the Christmas tree simply bought a new string of lights and hung the new lights over the old string attached at the factory to her synthetic tree. I did not see her tree and cannot say what the cause of the malfunction was. In the second occurrence we put up a synthetic tree with two strings of factory installed lights, one for the bottom half of the tree and one for the top half of the tree. The string on the top half worked some of the time, but then would go out. Typically one suspects a bad bulb. That is also the general suggestion made in the very fine article I linked above. However, that proved not to be the problem. Rather, the problem was the very cheap electrical plug. I cut the plug from the string so I could open it and determine exactly where and how it failed in order to satisfy my own curiosity. Installing a new male plug solved the problem. In the third case, my daughter had a string near the top of her tree that was "out," but not completely at the top. I had limited tools and resources, but plugging the bad string into a different molded female plug brought it back to life. The moral of the story is that while a bad bulb is a frequent source of problems, the molded male and female plugs on these inexpensive light strings are often held together only by a lick and a promise, and fail easily. Giving the molded plugs a hard look is much easier and faster than removing and testing bulb after bulb.

The first photo shows an extension cord with molded plugs from three strings plugged into the extension cord. The second photo shows the bad male plug on our tree, and I am using my multi-meter to test for continuity between the brass plug blade and the load end of one of the tiny fuses inside the plug. That part tests "good." The other fuse tested "good," too. In the third photo I inserted a straight pin into the wire and tested for a circuit from the brass blades to the wire. Both sides failed this test. 

A multi-meter can easily test what I needed to find this problem. I would have needed to strip away some insulation from the wire or stick a straight pin through the wire to obtain a reading with my multi-meter. But, by this time I had bought a hum tester with a high and a low range for checking different voltage ranges on an AC circuit. It led me to know the plug was the problem. 


Don't blame the incandescent bulbs, because I've had strings of LED lights that last for one season before parts of the string failed, but not necessarily at the ends. My problem in this case is that the first half of the string is out, and the back half is working. Also, the connecting string works fine. Any thoughts?

That depends on a few things...
1. Are the LED's connected in any way that would allow you acces them or the wires?
2. Do you have any testing equippment like a multimeter and know how to use it?

Problem with cheap LED strings, xmas lights or similar is that often quite a lot of LED's are put in series and share a quite high operating voltage.
Especially when coming from asia without any certificates in regards to electrical safety you might be surprised about the shortcuts taken to save a few cents.
In your case it could be as simple as a bad connection or as bad as a faulty LED or broken wire.
Depending on the construction on the lights (pics please!) you could use needles and a multimeter to check for the voltage on the LED's until you find the one that is broken or the part of the wire that is faulty.
You would have to poke the needles into the insulation of the wire until you reach the copper so it would not be suitable for any outdoor use after that.

I think IKEA is a world leader in pressboard furniture, which is usually only good for your current location, and pressboard doesn't last long in humid locations or wet environments, like real wood. Further, a thought based on holiday lights, I call them atheist lights because they are normally made in countries that are primarily atheists, and that includes all modern LED lights. If you support your country, don't buy from countries that are not friends of your country (which may lead to your not buying anything at all). The world is falling apart because all nations are in debt to China, and no longer manufacture or sell enough products from our own nations, to support the tax base required by our own governments. This also reduces good paying jobs within our countries.

I'm just amazed that people are still using incandescent bulbs!

In the case of our tree, we have had it for several years and it has always worked until this year. The lights are very firmly attached from the factory with zip ties. I expect you are suggesting LEDs are the way to go.

Absolutely - in the UK, it is very rare to find Christmas light that are not LED, and and IKEA area switching to supplying nothing but LED for their normal domestic lighting as well.

I doubt many people in the USA will put aside their functioning mini-lights until there is some incentive. Their mini-lights would need to stop working in a way that creates too much difficulty and expense to make them work again. The mini-lights would need to become unavailable. The mini-lights would need to become more expensive than LED lights. All of those things may happen one day, but that day has not yet come. As regards IKEA, I have been in one of their stores once and was very much unimpressed by what they offer. I know they have quite a following, but I am not a part of it.

Pricing must be different in the US, because I filled our front window with LEDs in selectable flashing patterns for about a fiver.

I could run them all night on a timer , without worrying whether they would start a fire, even though they rested on my curtains, and without worrying about the increase in my energy bills.

As for IKEA, whether you are impressed or not, where they lead, others follow.

(I saw a brief news article earlier today - apparently the Times Square countdown ball was all LED this time around, as has the display of the Empire State building - that will certainly drive future sales.)

Many municipalities in the USA are using LEDs for Christmas displays on lampposts and in public areas, as are commercial amusement parks. I do like the warm glow of incandescent bulbs for Christmas displays, though, especially at home. LEDs are colorful, but a little harsh.

Many years ago, when I was young (ie younger than now) I spent hours trying to run one of those strings of lights, with the idea that a power surge had burned one of the little lights, and with detect which was, the fault could be resolved. No, I was wrong: there were several lights out, about 4 or 5. The replacement of these few lights would cost more than a new wreath, so I bought one, and then kept the lights still worked, for repair future failures that NEVER OCCURRED AGAIN!.


Thank you for sharing your experience. It sounds all too familiar. I used two strings once on steel rod bent to look like Mary, Joseph, and a manger with a halo above the manger. About the third year I used it one string quit working. I spent a lot of time methodically testing, but never did get it working. My good news to share this time is that the problem may only be a bad plug easy to replace.