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What to do when half a string of lights is out?

It can be incredibly frustrating when you put up your holiday lights, plug them in, and find that only half the string is lit. Tracking down the culprit bulb or connection issue can be a tedious and time-consuming process. But with a few troubleshooting tips and tricks, you can get your lights back to their full twinkling glory.

First Steps

When half your string of lights isn’t working, the first thing to do is some basic checks:

  • Check that the lights are fully plugged into the outlet and that the outlet is working by plugging in something else.
  • Check that all connections between light string sections are secure.
  • Visually inspect the entire length of the light string to see if you can spot any obvious problems like broken bulbs or damaged wires.

If the lights pass these basic tests, then it’s time to move on to some more advanced troubleshooting.

Check for Loose Bulb Connections

One common cause of half a string going out is a loose bulb connection somewhere along the line. Start on the working side of the lights and gently wiggle each bulb to see if it causes any lights to go on or off. Keep working your way down the string until you get to the point where the lights cut out.

Pay close attention when you reach the last working bulb. Wiggle it gently and watch the non-working section to see if any lights flick on when you move that bulb’s connection. If they do, you’ve likely found the culprit. Tighten the connection on that bulb so it makes firm contact.

Check for Burnt Out Bulbs

Another possibility is that you have some burnt out bulbs scattered along the dark section of lights. The best way to check for this is to systematically replace each bulb in the non-working section one at a time. Unscrew the old bulb, screw in a known good replacement bulb from the working side, then check to see if that brings the section back to life.

If replacing a bulb doesn’t fix the issue, put the old bulb back in before moving on to the next socket. Make note of any bulbs that you replace that do bring some lights back on. Those are burnt out bulbs that need to be swapped for good.

Look for Shunts

Many light strings have special shunt devices built into the wiring between bulb sockets. These shunts allow the electricity to bypass any broken bulbs and continue down the line. But sometimes these shunts can come loose or stop working properly which blocks the flow of electricity.

Check for shunts along the non-working section and ensure they are firmly attached to the light string wires. You may need to use electrical tape to secure any loose shunt connections. Faulty shunts can also be bypassed completely by twisting the wires together on either side. Just be sure not to leave any exposed wires.

Test for Voltage Drop

As electricity travels down a long length of lights, some voltage can be lost due to resistance in the wires. This voltage drop can cause lights further from the outlet to be dim or fail to illuminate. You can test for this using a multimeter.

Plug in the non-working lights and touch the multimeter probes to the prongs of the plug. Note the reading. Then check the voltage at various points down the string, like every 10 feet. If the voltage steadily drops the farther from the outlet you go, then voltage drop is the issue. This may require shorter light strings or heavier gauge wiring to resolve.

Look for Damage

Carefully inspect every inch of the light string for any cuts, scrapes, or damage to the wiring insulation. Even a small nick in the wires can prevent lights further down the line from turning on. Use electrical tape to cover any faulty areas in the wiring. If there is damage over a large section, it may be easier to just replace that section or the entire string.

Isolate Sections

For long light strings, it can help to isolate sections to more quickly pinpoint issues. Start by unplugging from the outlet and separating the string into halves. Plug one half in and see if it works. If so, the problem must be in the other half. Continue dividing the faulty section in half and testing until you narrow down the exact point of failure.

Reverse the Direction

In rare cases, you may have a bad socket blocking electricity flow in one direction. You can test for this by plugging in the string starting from the opposite end. If the previously non-lit section now turns on, you have a bad socket that needs to be replaced. The electricity can only flow one way through that socket, which prevents half the string from working.

Replace the Fuse

Some light strings have a replaceable fuse built into the plug. Over time, these fuses can burn out and stop the flow of electricity. You’ll need to unscrew the fuse housing to check if the thin metal filament inside has broken. Any hardware or electronic store should sell replacement fuses for light strings that fit into the socket on the plug.

Look for Loose Plug Connections

Don’t forget to also inspect the male and female connections between the plug and socket. If these are loose, it could lead to intermittent contact that turns off half the lights. Carefully tighten the prongs on the plug and contacts inside the socket to restore secure connectivity.

When to Call an Electrician

If you’ve worked through all the troubleshooting tips above and still can’t get your entire light string working, it may be time to call in a professional. Any issues with voltage drop over long runs, damaged wiring in hard to reach places, or replacement of defective sockets are best handled by a qualified electrician. They have the proper tools and expertise to accurately diagnose and repair problems with your light strings.

Safety Precautions

When troubleshooting your holiday lights, make sure to take some basic safety precautions like these:

  • Always turn off power and unplug the lights before doing any troubleshooting or repairs.
  • Use a fiberglass ladder when checking lights installed up high.
  • Wear rubber-soled shoes and avoid standing on wet ground when handling lights.
  • Carefully inspect wires before plugging in to look for damage or fraying.
  • Never try to repair strings of LED lights, which require special handling.

Taking the time to properly inspect and fix issues with your holiday lights will save frustration and ensure your displays shine bright all season long. With a bit of troubleshooting know-how and some patience, you can tackle most lighting problems yourself. So don’t toss those half-working strands just yet – with a little effort you can get back to full lighting glory.

Preventative Maintenance

You can avoid many mid-season lighting headaches with some simple preventative maintenance:

  • When storing lights, carefully wind and tie them to avoid tangling and damage.
  • Check light strings for functioning and dirty/corroded sockets before hanging.
  • Replace any cracked sockets, frayed cords, or broken plugs.
  • Consider investing in good quality commercial or LED light strings.
  • Use plastic clips or hooks to avoid damaging insulation when hanging.
  • Hang lights properly on gutters or anchors to limit cord strain.
  • Use tie wraps to attach cords neatly and avoid loose connections.
  • Purchase adequate light strands to avoid overloading outlets.
  • Plug each strand into a grounded outlet protected by a GFCI.

Taking these simple precautions will help ensure your holiday lights provide years of bright, trouble-free service.


While troubleshooting half-working light strands can try your patience, a little perseverance and testing will usually uncover the root cause. Loose connections, burnt out bulbs, shunt issues, and wire damage are the most common problems that can leave you with dark strings. But with some basic tools and safety knowledge, you can tackle most lighting issues on your own. Just remember to always turn off the power before attempting any repairs. With the right approach and a bit of holiday spirit, your lights will be back to full glow in no time.

Light Issue Possible Causes Solutions
Half the lights are out
  • Loose bulb or shunt connection
  • Burnt out bulbs
  • Damaged wires
  • Voltage drop
  • Check/tighten connections
  • Replace bad bulbs
  • Inspect/repair wires
  • Test voltage down the line
Lights dim down the line
  • Voltage drop from long run
  • Too many strands on one outlet
  • Use shorter strands
  • Reduce number of strands per outlet
Intermittent flashing
  • Loose bulb or shunt connection
  • Damaged wires
  • Faulty sockets
  • Check/tighten connections
  • Repair wire insulation
  • Replace bad sockets
Entire strand doesn’t work
  • Bad fuse or circuit
  • Plug wiring issue
  • Faulty outlet
  • Check/replace fuse
  • Repair plug
  • Try a different outlet