Note: We’re re-publishing this post (originally published Dec. 2, 2016 and written by Taylor Whitney) because, well, it’s about that time again, and this post is a perennially useful answer to a very common question. While you’re gearing up for the holidays, be sure to check out our latest Gift Guide and follow us on YouTube, Instagram, or Twitter to catch our holiday deals.
Sometime in the near future you’ll venture into your dusty attic or musty garage and pull out a miserably tangled set of Christmas lights. As sure as Rudolph’s nose is red, one of those light strings won’t light up (if you ever manage to get them untangled in the first place). Millions will throw out their broken Christmas lights and buy new ones, but you will not. You are a strong, independent person. You will save Christmas (lights) this year.
Thankfully, it’s not too hard to fix Christmas lights. And iFixit’s repair community has already compiled lots of tips and tricks for how to do it—which I’ll be summarizing here.
Before you start
Make sure the lights are completely unplugged from any electrical socket before you start your repair. (Or you’ll be the Christmas ham.) You also need to know which kind of Christmas lights you have: Incandescent Christmas lights or LED Christmas lights. Incandescent lights work via a current running through a filament, which is different from their LED cousins. (Try here for LED light solutions.) This guide is for incandescent Christmas lights, so make sure those are the ones you have!
Before you can repair Christmas lights, you’ll need to identify the problem with them first. There are lots of different ways lights can break. If the entire chain is non-functional, a blown fuse could be the culprit. If a section of the light string isn’t working, there might be a bad bulb or a bad connection between the bulb and the socket (like a corroded socket). If replacing the bulb doesn’t work, it might be a bad socket or broken wiring that needs to be removed.
Here are some common ways to troubleshoot incandescent Christmas lights:
The string of lights won’t light up
Possible culprit: A blown fuse
The fix: Pick up the pronged “male” plug at the end of the strand. There should be a small door on the plug. Slide the door marked “Open” in the direction pointed by the arrow. Remove the two fuses, and inspect them by looking at them up against a bright background (the sky works). If the fuse is good, you should see an unbroken strand of wire running between the two metal contacts. (You can also use a multimeter to test for continuity.) Replace all blown fuses with new ones. Small fuses are inexpensive and can be found at most hardware, home improvement, or big box retail stores. Make sure that you read the specs printed on the non-functioning fuse so you can purchase the correct replacement. Fuse extraction can sometimes be difficult, stay patient! Try removing them like you would a battery.
Bulb won’t work or a section of the string won’t work
Possible culprit: A bad bulb.
The fix for small lights where the bulbs pull out: Gently grasp each bulb, and pull away from the socket. Once removed, inspect the bottom of the bulb and ensure that the two bulb copper leads are in their proper location (see picture below), and not twisted or missing. (You can also test bulbs for continuity with a multimeter.) Where you find a problem bulb, replace it with a new one. Continue with each non-functional bulb in the chain, up until you find the culprit(s).
The fix for large lights where the bulbs screw out: Gently unscrew each bulb and remove them from the socket. Replace the one you just removed with a new bulb and test the light strand. If the strand still has the issue, you can put the old bulb back in the socket and continue on down the line until you find the culprit(s).
String won’t light up—replacing a bulb doesn’t fix it
Possible culprit: Corroded socket
The fix: Over time, the contacts inside the socket can become corroded or filled with dirt and grime. This damage can prevent proper contact between the bulb and the socket, which often results in no power to the bulb. Use a small file or scratch brush to clean the wire contacts of the socket. Once the socket is clean, insert a new bulb into the socket.
I’ve tried everything and a bulb or section is still not working
Possible culprit: Bad socket or wiring around a single bulb.
The fix: If all else fails, the bulb socket may be broken beyond repair. Removing it isn’t too complicated though, and should restore functionality to the rest of your lights! There are two potential ways to you can approach this repair.
Using a wire connector: Use a wire cutter to remove the defective socket from the light strand. Strip about 1/2″ of insulation from both wires. Twist the wires together and insert them into a waterproof wire connector. Turn the connector several times until the cap feels secure, and you can tug on it without it falling off. If replacing the bad socket fixed the problem, consider putting in some silicone sealant into the cap in order to keep moisture out and prevent the wires from corroding.
Using weatherproof heat shrink tubing: Use a wire cutter to remove the defective socket from the light strand. Strip about 1/2″ of insulation from both wires. Solder the wires back together or make a western union splice. Then follow the instructions in our How to Use Heat Shrink Tubing guide to protect the wires.
crwdns2944067:011crwdne2944067:0
I have an incandescent pre-lit tree with multiple plugs within the tree that daisy-chain together. When each strand is plugged in individually to the wall, everything works; but when I plug them together there is one strand in the middle of the tree that does not work. I’ve used the Light Keeper Pro tool to check the voltage in the strand and it seems to check out throughout the whole stand even when the lights aren’t working. It doesn’t seem like this is an issue with the male portion of the plug since it works fine when plugged in elsewhere. Maybe there’s something wrong with the female portion that it’s getting plugged into? The strand on the other end of that plug works fine. None of the trouble-shooting lists seem to cover this.
Thank you!
Linda M - crwdns2934203:0crwdne2934203:0
I have a home accents pre-lit Christmas tree. I have a stand that nearly every bulb in 1/2 if it was burned out. I finally traced it back to a bulb that has a different base/collar and I can't get the bulb out. I accidentally broke it trying to pull it out. When I grab the two wires that were inside that bulb with a pliers, the whole string works, but the lights are twice as bright as the other strings on the tree. Could that be a resistor or step down transformer of some kind? I could send a picture of it if anyone could help? Thanks in advance.
Fredrick Boening - crwdns2934203:0crwdne2934203:0
There’s this greenish Santa in my living room telling me one of the lights on my tree doesn’t light up on one side. Should I let him take it back to his shop to fix it?
Steve - crwdns2934203:0crwdne2934203:0
If it’s not an LED strand, step 1 should be “throw the whole strand away” and step 2 should be “Buy and LED light strand. Seriously, I know this is iFixIt, but incandescent strands not only use much more electricity (and can pose heat/fire issues in the larger bulbs) but are an absolute nightmare to deal with (particularly the minis). You can go one-by-one, pulling bulbs, moving the tiny wire leads, checking for corrosion, etc., and putting them back, only to find you’ve gone through the whole section or strand and nothing’s changed. Were there two bad bulbs/sockets? Any strand where one bulb takes out 25 (or all) other lights is total crap. I suppose if you’re retired and have nothing better to do with your life, you can spend forever trying to make it work vs. spending $3-$5 (especially after Christmas) on a new set. Enjoy!
Timothy Hood - crwdns2934203:0crwdne2934203:0
I am a tech savvy technician. Unfortunately, the greatest amount of input to repairing these lamps ( That I have done year after year) is TIME! and if you balance the amount of time spent repairing these things—there is NO PAYBACK! This year I just recycled sever sets to the round bin, and purchased new at only $3.98 per set. YET Stupid and wasteful- like so many OTHER repairable items we toss daily. So, the real engineering here is to have makers of lights build a better product. Go ahead! Corner the market. It is up to US to find a better solution. Xmas lights! Bah, Humbug! Get a laser projector! Anything other than these problem prone light strings!
James Simpson - crwdns2934203:0crwdne2934203:0
I have kept 10 exterior trees in Xmas lights (+5 strings on each tree) for at least 10 years at our row condo in Ottawa Canada. All of our light strings are now LED. The incandescent strings took too much power and bulbs are hard to get, so we have switched to LED.
I use a product called the LED Keeper to fix the strings. They also have an incandescent tester available.
The LED Keeper is very good at finding bad connections and bulbs. I got one at a post Xmas sale (sale price ) and have used it for about 10 years. I had to replace the wire piercing pin, which they replaced (for a fee) and am very happy with it!
It also has a fuse test point and a LED test, remember LEDs only light up in one direction, so try both directions.
If you can get it at an Xmas sale - well worth it, if not, still a good deal especially if you are keeping multi strings working!
MikeD
MikeD - crwdns2934203:0crwdne2934203:0
While I agree that switching to LED is the way to go, if you have a pre-lit tree with incandescent bulbs, you can use the “Light Keeper Pro” tool to easily fix broken strings (or other work-alike tools). You don’t have to search for the burnt out bulb — this tool sends a pulse of high voltage into the string which causes the broken bulb to short out and all the other bulbs magically start working. It worked great for me for many years, Eventually we replaced the old pre-lit tree, but it allowed us to get a bunch more years out of it and save money. https://www.amazon.com/Pro-Repairing-Inc...
anonymous 4196 - crwdns2934203:0crwdne2934203:0
In an early step the author says you can check a bulb for continuity, but that’s misleading. Today’s strings are designed with shunts at the bottom of the filament base. You will see continuity even if the filaments are blown/broken.
Hafcanadian - crwdns2934203:0crwdne2934203:0
How about an article about fixing today’s multifunction LED sets. With a control module up front and lamps with 4 wires instead of 2, the things drive me nuts trying to diagnose, and there’s next to nothing anywhere about repairing them. Indeed they are more expensive than most, so not easily discarded.
Hafcanadian - crwdns2934203:0crwdne2934203:0
What could cause christmas tree lights to keep blowing the fuses in them? I have a large real tree & use 10+ sets of lights. I got them on & everything worked fine. A short time later some sets went out. I found the last one connected to the ones still working & replaced its fuses. This has happened 6 times. I have tried using different outlets. I have tried using a different extension cord. It's driving me crazy!!!
bce1950@yahoo.com - crwdns2934203:0crwdne2934203:0
I am finding that the most common difficulty is the connection from the string for the lights to the little transformer /control unit. In one case the connector itself is inexlicably dead (I've tried swapping in same make units from other strings to ascertain where the problem is) -maybe wear and misalignment? And in another couple of cases the wire has snapped but the power transformer unit that gets plugged into the wall socket is a sealed unit so I can't get into it to reconnect the wires -unless someone has a clever fix?
Andii - crwdns2934203:0crwdne2934203:0