Understanding How String Lights Work
Understanding how your lights work is the first step to figuring out what’s wrong with them. String lights operate on a dual parallel circuit system, with each string containing:
One circuit powering the lights
Another circuit carrying power to the next string
Three wires join the circuits at the middle and ends
Due to this design, you'll never see just one bulb out - it will always be half the string or the entire string.
Common Reasons Your String Lights Won't Turn On
Faulty Coaxial Adapter or Blown Fuse
Each coaxial adapter contains a fuse that acts like a circuit breaker. To check the fuse, look for a small thin silver line for a healthy fuse.
A shattered fuse could indicate power surge damage.
How to fix it:
Replace the blown fuse with a new one. Each String Light Adapter comes with a spare fuse.
Check the electrical load on the circuit by calculating or using a multimeter. A light string adapter is rated to a maximum of 8 amps, but it's wise to keep the load to 30% below this threshold for safety reasons.
2. Severed or broken wiring
This is the most common issue, and could be very noticeable or almost invisible. Here's what to look for:
Completely severed wires (easily visible)
Small cuts exposing copper wire (less visible)
Damage from staples or mounting hardware
Even minor damage can cause failure when exposed to moisture.
3. Malfunctioning Rectifiers
Rectifiers join parallel circuits at three locations:
Beginning of the string
Middle of the string
End of the string
Components in the rectifiers could become faulty over time, so if neither of the two problems above are the issue, this one might be the culprit. This is sometimes identifiable when half a string is out.
Troubleshooting Scenarios
Safety Reminder: Always disconnect power before handling or inspecting lights, and use appropriate safety equipment when working at heights.
What to do if the Whole Display is Out
Check that your power supply is working correctly
Examine the fuse in the coaxial adapter
Replace fuse if needed
If the new fuse blows immediately, there may be a faulty string of lights causing the issue. You'll need to track down the string of lights that is causing that fuse to blow, and replace it.
Pro Tip: How to locate a faulty string
If you are working on a tree, start by dividing the tree into sections, usually at the base of the branches, and use an extension cable to test each section, tracking down your faulty string.
If Half the Display is Out
This will likely caused by a malfunctioning rectifier
Locate and replace the faulty string
Pro Tip: If the third rectifier (at the end of the string) is faulty, the string itself might be on, but the following string will not be receiving power properly, so the issue is actually with the string prior to the string that is out.
Weather-Related Issues - If the lights are out after a heavy rainfall or snowfall
Extreme moisture can cause havoc on your installations, and keep in mind that moisture levels tend to be higher the closer they are to the ground.
Raise connections 4-6 inches off the ground
Keep connections away from areas where moisture collects
Allow connections to dry completely before testing