How to Fix Christmas Lights

Verify Power Runs to Outlet

All Christmas lights plug into a wall outlet for power. If no power is running to that outlet—or if the power is there but not getting to the lights—then the lights will not work.

Locate your home's electric service panel. This is a box with a metal door, and it is typically located in garages, basements, mudrooms, or in other areas that are out of the way but not hidden.

Locate the circuit that should be sending power to the outlet. Gently rock the circuit breaker switch toward the center of the panel. If the switch feels springy, it has been flipped off and no power is running to the outlet.

Rock the switch backward (toward the outer edge of the box), then back again toward the center. The switch should engage and send power to the outlet again.

Verify Outlet Has Power

Go to the outlet again. Even if power is running to the outlet, the outlet may not be delivering power to the Christmas lights.

1. Slide the light string plug in and out of the outlet. If it moves easily, the outlet may be old and the inner copper contacts are not touching the outlet's prongs. Replace the outlet.
2. Is the plug extremely tight? If so, this may be a tamper-resistant outlet. This is identified with "TR" on its housing. These outlets often grab the outlet too hard, making contact difficult. Push the outlet the rest of the way in.
3. Is the outlet a GFCI outlet (identified by two buttons on the face)? Reset the button. You can test to make sure that your GFCI outlet is working correctly with an inexpensive GFCI tester.

Check Christmas Light Fuse

One benefit of owning up-to-date Christmas lights is that they often come with an additional safety device: an on-board fuse. First, unplug the lights.

You'll find the fuse (or two) located in the cord's plug. With the flat-head screwdriver, slide open the door. Remove the tiny, cylindrical fuse.

Hold the fuse up to the light. If it is brown or black inside or if the filament is visibly severed, the fuse likely no longer works.

Insert a replacement fuse and plug the lights in again.

Check and Re-Seat Bulbs

Individual bulbs in the string may be loose or they may be burned out. One way to check for this is to start at one end of the string and methodically go from bulb to bulb, pressing each bulb in and looking for obviously burned-out bulbs.

A more effective, less time-consuming way to essentially do the same thing is to use a Christmas bulb tester. First, make sure that the tester itself is working. Then, with the lights plugged in, turn on the tester and slowly pass it across the entire run of lights.

The tester will emit a constant sound and sometimes a light as long as it detects voltage. Once the tester reaches an area with no power, the beeping will stop.

Pull the bulb straight out. Do not twist. Push the fresh bulb straight in.

Fix Lightbulb Shunt

Broken filaments aren't the only cause of bulb failure. Each bulb contains a secondary element that acts as a backup to the filament: the shunt. The shunt is designed to keep the electricity flowing, even if the filament is broken.

When the shunt fails to work, the entire string of Christmas lights fails.

There are a few tools that can repair failed bulb shunts, including one is called the Lightkeeper Pro. By squeezing the trigger of this device, you can repair bulb shunts. The Lightkeeper Pro can detect voltage within the line.