Christmas tree light bulb tester and repair tool (Optional)
Multimeter (Optional)
Fine-grit sandpaper
Microbrush
Small screwdriver
Picture this: At the start of the holiday season, you unpack your seasonal supplies, only to discover that half of the Christmas lights are no longer working. This kind of disappointment can put a damper on the festivities, which is why it’s helpful to know how to fix Christmas lights that are half out.
Don’t run out to buy new lights yet. In many cases, when only half of a strand has gone out, you can repair Christmas lights yourself and restore your festive illumination. Let’s review how to repair half-out Christmas lights.
Determine LED vs. Incandescent Bulbs
Incandescent Christmas lights are hardwired in a series on two or more continuous circuits. When a bulb in the middle of the strand goes out, the circuit isn’t complete and the lights that follow won’t receive the proper voltage. LED lights are more durable, and when only part of a strand goes out, the issue most likely resides with one of the fuses.
Consider Purchasing a Christmas Light Bulb Tester
These devices typically cost between $25 and $30 and will make your job significantly easier if you need to track down one bad bulb on a strand. You can also test the bulbs with an electrician’s multimeter tool, but Christmas light testers include additional functions, like voltage detection, bulb removal, and shunt replacement. You don’t need a dedicated bulb testing device to diagnose and fix your faulty strand, but it could save you time and hassle.
Clean the Plug Prongs
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Sometimes corrosion on the prongs of the electrical plug is the culprit for a partial outage. Since it’s the easiest cause to diagnose or rule out, it’s best to start here. If you see dark spots or debris on the prongs, try cleaning them so that they can conduct the proper voltage. Spray on a commercial cleaner that’s safe for electrical contact and scrub it off with a microbrush.
Alternatively, you can rub the corrosion off with a piece of fine-grit sandpaper. Once you clean the visible accumulation, wipe down with a clean cloth to remove any sanding dust. If some of the lights are still not turning on after you plug it back in, move on to the next step.
Examine and Repair the Fuses
With incandescent Christmas lights, a blown fuse usually results in the whole strand going out, but with LED lights, you can potentially fix it with a new fuse. Look for an indented compartment on the plastic casing for the plug on the prong end of the strand. Using a small screwdriver or your fingernail, slide it open toward the prongs. You’ll find two small fuses inside. Delicately lift each fuse from the bottom and pop them out.
If the glass on either of the fuses looks stained or dark, it's likely blown. If both fuses appear normal, go ahead and replace the fuses. Ensure your new fuses are the same size and amperage as the previous ones. Luckily, nearly all of them are rated for 3 amps. Use gentle pressure to slide the new fuse into the proper compartment until it clicks into place. You may need a small tool, like the tip of a pen to safely insert it. Close the compartment and plug the lights back in to test them. If a section of the lights remains dark, move on to the next method.
Inspect the Lights
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If the fuses and prongs aren’t the problem, it’s safe to assume a bad bulb is the source of the issue. The first step toward locating the broken bulb is visually inspecting the whole strand. Look for bulbs with damage, have gone missing, and look unusual in some way.
Another telltale sign of damage is silver- or black-colored staining on the inside of the bulb. Smoky-looking bulbs mean the amperage rating for the strand had been exceeded because it’s connected with too many other strands. Make sure to consult the rating on your set and avoid overloading the wire in the future.
Identify Loose Bulbs
If your inspection hasn’t yielded any results, your next move is to check the strands for any loose bulbs. Plug the strand back in and, starting with the first unlit bulb, wiggle each one with your fingers or flick them gently with a pencil. If lights flicker when they move, it’s safe to assume it’s loose. Unplug the strand and gently press the bulb back in until it clicks into the socket. If that step has not resolved the issue after you plug the strand back in, you’ll need to replace the bulb.
Test Every Bulb
Photo: ThreeJays / E+ / Getty Images
After trying the other strategies, you have no choice but to check every bulb for damage. This task is significantly easier with use of a Christmas light bulb tester. These inexpensive tools often resemble a small pen. Touch the device to each bulb, and it will light up or beep when it reaches a malfunctioning bulb.
Change Any Bad Bulbs
Before attempting to remove or add any bulbs, fully unplug the strand—otherwise, you risk electrocution and serious injury.
Some light strands feature a small plastic latch on the bulb seat. If that’s the case, lift the latch and leave it in the open position. Take the plastic seat of the bulb between your fingers and gently squeeze upward, lifting the seat and the bulb out of the socket together. Avoid pulling the bulb so you don’t damage the wires.
Replace the bulb with a spare from the kit or a new one from the same manufacturer. Trying to force a bulb onto a strand that doesn’t match can lead to a short and, in some cases, fire damage. Slide the new bulb into the socket and gently but firmly press it into place. Plug the string of lights in to confirm that the new bulb works and the connection is restored.
Repair a Damaged Shunt
Photo: Kinga Krzeminska / Moment / Getty Images
If the whole strand doesn’t light up after you’ve replaced the bad bulbs, the cause of the problem is likely a faulty shunt. The shunt is a small device that offers a low-resistance path for the electrical current to pass through the circuit and reach each bulb.
You’ll need to use a Christmas light repair tool to repair a damaged shunt. Start by removing the bad bulb. Insert the socket into the repair tool (or vice-versa, depending on the model you’re using), and squeeze the trigger once or twice, per the manufacturer’s instructions. This action shoots a series of pulses through the circuit that should reactivate the shunt. Return the replacement bulb to the socket and plug the strand back in.
DIY vs. Hiring a Pro
In principle, you could hire a local handyperson to repair malfunctioning Christmas tree lights, but it will likely cost more than replacing the strand. Repairing damaged holiday lights is a simple DIY project that can help you save money on Christmas lights. Keep in mind that Christmas lights are designed to burn brightly for a short while before being swapped out for an affordable replacement set. To avoid future repairs, consider hiring a Christmas lighting professional who can disassemble and store your lights correctly.
Frequently Asked Questions
If only half of your string of Christmas lights is out, it likely means that you have a broken or loose bulb somewhere along the strand. That’s why we suggest inspecting and testing each bulb to ensure it’s still tight and functioning properly. Luckily, this problem is quickly solved with a DIY fix, such as replacing the bad bulb or repairing a damaged shunt.
An affordable Christmas light bulb testing and replacement tool can make the job easier. But you can most likely make all necessary repairs yourself using common toolbox items if you’d rather avoid purchasing another gadget.
You can take a few steps to prolong the life of your holiday lights. Make sure to replace burnt-out bulbs as quickly as possible to avoid overloading the rest of the circuit and knocking out more lights. Before packing them up each year, plug each strand into the wall to confirm everything is still working. Wrap the lights carefully back into their original packaging or something similar—winding a strand tightly together or leaving it to hang loose in a storage bin can lead to frayed or damaged wiring.
While Christmas lights are a wonderful way to light up your home during the holiday season, they don’t have a long lifespan. Most incandescent Christmas light bulbs are designed to last between 1,000 and 1,500 hours—or about one to three holiday seasons. More durable LED bulbs should last about 10 times as long.
A professional content writer, C.E. has written about all things home, family, and wellness for a variety of publications, including HomeLight, Noodle, and Mimi. A third-generation Los Angeleno, she is always looking for ways to make the most of the sun, whether it be building an urban garden or decorating with the help of some low-maintenance, air-purifying plants.
A professional content writer, C.E. has written about all things home, family, and wellness for a variety of publications, including HomeLight, Noodle, and Mimi. A third-generation Los Angeleno, she is always looking for ways to make the most of the sun, whether it be building an urban garden or decorating with the help of some low-maintenance, air-purifying plants.
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