How to Troubleshoot Holiday Lights

It's that time of year again: You have to pull out last year's holiday lights to determine which lights work, which lights you can fix and which strings to toss. If you're a DIYer who'd rather repair strands than buy new, try TOH's tips for troubleshooting Christmas lights.

The key to working lights is a power source, good fuses, lights and wires. If one part of this chain is broken, so are your lights. It might sound obvious, but your first step should always be double-checking your power source. Make sure circuits are turned on, and the plug is live.

Next, check your bulbs. In series strings, one bulb can burn out the whole strand. Troubleshooting burnt-out bulbs by hand can be a tedious process: You have to find problem lights by trial-and-error. Another tip: Make sure all bulbs are properly screwed in-sometimes a too-loose light can be the culprit that kills a whole string.

For an easier way, try a tool such as the LightKeeper Pro. This hand tool plugs directly into the string, and sends a quick jolt of electricity through the strand. The electricity repairs the light bulb's shunt (the device that allows electricity to pass through points on a circuit) and usually fixes defective bulbs in seconds.

Read the rest of This Old House's tips on troubleshooting lights at

Before you begin working with lights, read TOH's tips on holiday-light safety. For inspiration on how to decorate once your lights are fixed, check out our collection of Christmas lights gone wild.