How to Fix Christmas Lights

Replacing a Blown Fuse

Try this if the entire string goes out. A blown fuse will turn the entire string dark, not just part of it. This often happens when too many strings are connected end-to-end. A fuse can also blow when the wires are accidentally stapled during installation, or when the lights are plugged into a socket with too high a voltage (such as US lights in a UK socket). If only some of the lights are dark, the fuse may be good. Skip down to replacing the bulbs instead.

Open the fuse case. A string of Christmas lights typically has one or two tiny fuses in the plastic box attached to the prongs. Examine the plastic closely on the side of this box and in between the prongs for a cover you can slide or pry open with a small flat screwdriver. These often get stuck, so you may need to use some force. Do not plug the lights back in at any point during this method.

Check the fuses. Each fuse should be transparent, with an unbroken wire running through each one. If a fuse is black, or if the wire inside is broken, it needs to be replaced. You may need to remove the fuse and hold it up to a bright light to inspect it.

Pry out the blown fuses. Gently lever the blown fuses out with a thin screwdriver or other convenient flat implements like a pen knife.

Find an exact replacement. Many Christmas lights are sold with spare fuses for this purpose. If your spares have escaped from the holiday box, take the blown fuses to an electronics store and ask for a replacement. 100-light strings typically use 3A fuses, but it's best to confirm your fuses' rating with a store employee. Never use a fuse with a higher rating. This can cause a major fire risk. Some LED lights only require one fuse, but keep a second one in the plastic compartment as a spare. If there's a fuse that's not attached to any wires, just transfer it over to the other slot.

Put in the new fuses. Pop the new fuses into the slots and close the plastic cover. Plug the light bulbs in to see if this has fixed the problem. If the lights still won't come on, try a different outlet in case you blew a house fuse or circuit. If that doesn't work, keep reading for other solutions.

Finding the Dead Bulb (Storebought Tools)

Buy a christmas light repair tool. Most of these tools include everything you need to find and replace the bad bulb: a continuity detector, piezoelectric sparker (shunt repairer), and light bulb removal tool. It costs roughly $20 US, so this may not be worth it if you only have a couple strings of lights. If you prefer to avoid buying such a specialized device, try the following alternatives: Get a non contact voltage detector and skip down to tracing the dead bulb. Alternatively, buy a cheaper light bulb tester without the other features. Tackle the project hands-on with a homemade tool.

Use the spark function on your repair tool. Christmas lights are connected in series, meaning the whole string will go dark when one bulb fails. A failsafe called a shunt in each bulb is supposed to prevent this by closing the gap across the burnt-out bulb, but these often don't work properly. (In regions on 230V mains rather than 110V, the shunt usually does its job.) The sparker function on your repair tool will zap the shunt, hopefully succeeding in closing the gap: Plug the string of lights into the socket on the repair tool. Press the button (or pull the trigger, depending on the model) about 20 times. You should hear a click each time. Plug the string of lights into a normal outlet. If the string is still dark, continue to the next step. If the string lights up except for one or two bulbs, skip down to replacing individual bulbs.

Trace the location of the dead bulb. If the string of lights still won't light up, move on to the detector. This detects the current running through the wires, so you can identify the point where it fails. Here's how: Tug apart the braided wires to identify the one directly connected to the light bulbs. Place the detector on this wire about halfway along the string, between two bulbs. (If your tool has a small hole for a detector, place a light bulb into the hole instead.) If the tool hums or lights up (depending on model), the problem is in the half of the string farthest from the plug. If there is no hum or light, the problem is in the half closest to the plug. Move the tool to the middle of the problem area and test again, narrowing it down to ¼ of the string. Repeat until you find a bulb with current on one side of it and no current on the other. Mark this bulb with tape so you don't lose track, then replace this bulb as described below.

Finding the Dead Bulb (DIY)

Understand the goal. Each Christmas light bulb has a "shunt" that is supposed to close the gap when the bulb burns out. This often fails, but a small surge of current can trigger this and put your lights back on. This will not work every time, especially with this DIY approach. If you're looking for quick results, try the methods above instead.

Find a lighter operated by button. This type of lighter has a piezoelectric crystal which creates a spark when pressed. Do not use the type with a metal wheel, which creates the spark through friction.

Empty the lighter of fuel. If the lighter is disposable, just burn the fuel away. If the lighter is refillable, transfer the lighter fluid to another lighter, or to a sealed, clearly labeled fire-proof container. Never dispose of lighter fluid in a drain or in household trash.

Remove the piezo igniter. Pry apart the plastic cover, then lift out the igniter with a pair of needle nose pliers. The piezo igniter includes a button, and two tiny metal or plastic prongs. When the button is pressed, a spark jumps between these prongs. The spark is not dangerous, but it will give you a mild electric shock. More importantly, it could ignite fumes and light a small flame. Work over a nonflammable surface and keep your fingers and face away from the sparker during removal.

Zap the prongs of the light string. Position the two prongs of the sparker against the two prongs of the Christmas light plug. Push the button about 10–20 times. You should hear a click and see a spark each time. If it's too hard to line up the prongs, connect them with insulated wires.

Plug in your lights. If all went well, the lights should now light up. There will be one or two dead bulbs, which should be replaced as described below. Leaving the dead bulbs on will cause the other bulbs to burn out sooner.

Replacing Individual Bulbs

Twist the light bulb to check the connection. This is rarely the problem, but it only takes a second to check. Twist the light bulb gently to tighten it in position. If the bulb moved noticeably, plug in the lights and see if a loose connection was causing the issue. Assuming the bulb is still out, continue to the next step. If you have many lights, buy a string of bulbs of the same brand and type. Keep it in storage and twist off the bulbs to use as replacements when you need them.

Purchase replacement bulbs. If you don't have any replacements, take along the burnt-out bulbs to a hardware store, pharmacy, or home improvement store. Look for bulbs that match as closely as possible. Ideally, check the packaging your lights came in to see what type of bulb is needed. Some bulbs are flashers, and when installed, will cause lights to flash on and off. There is no need to have two flashers on the same circuit, as they may cause unusual on / off timings.

Remove each of the blown-out Christmas light bulbs. Use your thumb and index finger to delicately put pressure on each of the broken light's plastic base, to remove the fragile bulbs. If you have a Christmas light repair tool, it may come with a small grip for this purpose. In order to remove a broken Christmas bulb from its socket, find the two copper wires that sit on the base of the old bulb, noting their position on the base. Push both of the copper wires down, so that they are pointing towards your floor, and the bulb is pointing towards the ceiling. Pull upward on the bulb, and it should now be separated from the light's base.

Insert the replacement bulb into the old bulb's socket. Make sure the two copper wires are completely aligned with the holes in the bulb's base. Once the bulb is fully seated in the base, fold the copper wires against the base in the same position as noted above. Plug in your lights and watch them glow. If you used a continuity/voltage detector tool, and your lights still won't turn on, use the tool again. There may be a second burned-out bulb. These tools can only detect one burned out bulb at a time.

Remove broken sockets. If a new bulb still won't light up, your socket may be corroded or the wire may be damaged nearby. Removing this is not as difficult as it sounds, although each bulb you remove will cause the remaining bulbs to burn more brightly and therefore burn out sooner though removing one or two bulbs should be fine. (Note that a damaged wire or a repair using this method, unless done well, may present an electric shock or fire hazard. If you don't feel comfortable removing light bulb sockets, then you can just leave a light bulb in the socket or cover it with electric tape to prevent an electric shock.) Follow this method: Unplug the lights. Using wire cutters, cut the wire on either side of the broken socket. (Do not cut the other two wires.) With a wire stripper, strip about ½ inch (1.25cm) of insulation from each cut end. Twist the two strands of wire together. Get a twist connector from an electronics store (a small conical cap). Twist this over the wire, holding it in place.