Quck answer
To fix Christmas lights with a multimeter, follow these steps:
1. Plug in the lights and check if any bulbs are not lighting up.
2. Set the multimeter to the resistance mode.
3. Remove the bulb and place the multimeter probes on the bulb’s metal contacts.
4. If the multimeter shows a reading of infinity, the bulb is burnt out and needs to be replaced.
5. If the multimeter shows a low resistance reading, the bulb is working fine.
6. Repeat steps 3-5 for each bulb until you find the faulty one.
7. Replace the faulty bulb with a new one and retest the lights.
8. If the problem persists, check the wiring connections and fuses for any issues.
String lights are commonly used to adorn trees or as outdoor decorations during the holiday season. However, they tend to malfunction after being stored for a long time. This is usually caused by a single bulb that can make an entire section or the entire string of lights go out. Instead of throwing the entire string away, you can use a multimeter to check for failure and to locate the faulty bulb. If it’s not a burned-out bulb, the issue may be a blown fuse, which is easy to fix.
How to Check Continuity with a Multimeter
Image Credit:
Leigh Schmidt for Hunker
To check Christmas lights with a multimeter, you cannot perform a voltage test with a noncontact voltage detector. Instead, you can use the multimeter to check for continuity, which measures resistance. You can do this while the string is unplugged, making it safer. A complete electrical circuit allows electricity to flow with little resistance. If there is a break in the circuit, the resistance will be high or infinite.
Start by checking the resistance from one end of the string to the other. The circuit consists of a hot leg that runs through all the bulbs and a return leg that bypasses the bulbs and extends from the male plug to the female plug. The return leg should have low or no resistance. If it doesn’t, the wires are damaged, and it’s best to dispose of the string. You can also perform a continuity test on individual bulbs until you locate the faulty one. This may take a few minutes, but it’s a more efficient method than going from bulb to bulb.
Testing String Lights for Continuity: A Step-by-Step Guide
1. Prepare the Multimeter
Image Credit:
Leigh Schmidt for Hunker
To begin testing your string lights, set the multimeter to the ohms (О©) of resistance setting. Insert the black lead into the common (COM) socket and the red lead into the volts-ohms (VО©) socket. Touch the leads together and ensure that the resistance reading is zero.
2. Test for Continuity
Image Credit:
Leigh Schmidt for Hunker
Unplug the string lights and insert one of the multimeter probes into a slot on the female plug end. Touch the other probe to one of the prongs on the male plug end, then repeat the process with the other prong. The meter should read zero, indicating continuity.
Next, move the first probe to the other slot on the female end, and test both prongs again. One of the tests should read zero, confirming that the wiring is intact. If neither test yields a zero reading, there may be a break in a wire or blown fuses.
3. Locate the Fuses
Image Credit:
Leigh Schmidt for Hunker
If the continuity test fails, check the fuses in the male plug end. Locate the “OPEN” door on one side of the plug, between the prongs, and slide it towards the prong end to expose the fuses.
4. Inspect and Replace Fuses
Image Credit:
Leigh Schmidt for Hunker
Remove the fuses by prying up one of the metal ends with a small flat screwdriver. Examine each fuse against strong light; if the glass cylinder is blackened or the filament inside is broken, the fuse has blown and needs to be replaced.
5. Replace Blown Fuses
Image Credit:
Leigh Schmidt for Hunker
Use spare fuses from the plastic bag that comes with most light strings or borrow one from another string with a similar size. Replace any blown fuses and close the access door before testing the string lights again. If continuity still cannot be achieved, it might be time to replace the string lights.
Tip
If you cannot determine which bulb is faulty, test each bulb individually for continuity with the multimeter. Start from one end and work your way to the other end.
1. Remove the Bulb
Image Credit:
Leigh Schmidt for Hunker
To remove the bulb, hold the socket of the bulb firmly with your thumb and forefinger. Use your other hand’s thumbnail to pry the plastic ring at the bottom of the bulb. Make sure not to pull the clear glass part of the bulb. Once the bulb is loose, take it out carefully and place it on your work surface.
2. Test the Bulb
Image Credit:
Leigh Schmidt for Hunker
Observe the two small wires that extend from the bottom and fold up along each side of the plastic bulb base. Use a multimeter to touch one probe to each of the wires, making sure not to let them touch each other. Sometimes, you may need to press inward with the probes for a reading.
Check the meter readout. If the reading is close to zero, the bulb is good. If you get a high resistance reading (indicated by “1,” “OL,” or “Open Line” on digital meters), the bulb is faulty.
3. Replace or Reinstall the Bulb
Image Credit:
Leigh Schmidt for Hunker
If the bulb passes the continuity test, push it back into the socket. Note that the base of the bulb has flat sides that match the socket’s shape. Push the bulb in until it snaps into place.
If the bulb fails the continuity test, you can replace it with a spare bulb from the bag that usually comes with holiday lights. If you don’t have a spare, you can use a bulb from an old string or dedicate a new string for this purpose.
Tip
If you want your Christmas lights to last longer and avoid the hassle of troubleshooting every few years, consider upgrading to LED Christmas lights. LED bulbs can last up to 50,000 to 100,000 hours, while incandescent bulbs only last about 1,200 hours.