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Use a Christmas Light Tester to Check Holiday Lights

A simple tester helps you fix holiday light strings fast

FH07DJA_TESLIG_01-2Family Handyman
Find a holiday light problem and fix it fast with this simple tester and repairer. You don't have to test every bulb!

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Test and fix bad strings of holiday lights

Photo 1: Fix a bad Christmas light string

Remove a bulb from an unlit section, plug the empty socket into the connector, plug the string into an electric outlet, then squeeze the trigger until the lights turn on.

Photo 2: How to find a bad bulb in Christmas lights

Press down the black button, hold the tip about 1/2 in. from the string, and move it along the cord until it stops beeping (at the defective bulb).

There’s a way to test (and fix) the entire string of miniature lights without testing each bulb individually. Try the LightKeeper Pro ( It’ll identify and oftentimes fix most problems in miniature and icicle light sets (but not the sets of larger lights or LED lights) with a few squeezes of the trigger (Photo 1).

The trigger sends an electric charge through the circuit to repair internal bulb failures. (The “shunt” in the bulb is supposed to act as a bypass if a filament fails to complete the circuit. If the shunt fails, it knocks out the lights in the section. The electricity sent by pulling the trigger locates and fixes the defective shunt.)

If that doesn’t work, hold down the black button on top of the tester and move the tip along the string so it beeps (Photo 2). Note where the beeping stops, then replace the previous bulb.

The tester is available at home centers and some hardware stores for about $20 (find retailers on the company’s website).