How to Use a Light Tester to Fix Christmas Lights

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A simple tester helps you fix holiday light strings fast.

One broken bulb on a strand of christmas lights can render the whole string completely useless. Good news, though: there’s a way to test (and fix) an entire string of miniature lights without having to check each bulb individually. Try using a device like 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.

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Fixing the Shunt

Here’s how it works. First, you remove a bulb from an unlit section of your lights. Then you plug the empty socket into the LightKeeper, plug the string into an electric outlet, then squeeze the trigger until the lights turn on. The trigger sends an electric charge through the circuit to repair internal bulb failures. Something called 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 LightKeeper’s trigger locates and fixes the defective shunt, allowing the rest of your light strand to light up as intended.

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Finding the Dead Bulb

If that doesn’t work, you can also use the LightKeeper to locate and replace any defective bulbs that might be keeping your light strand from illuminating. You just hold down the black button on top of the tester and move the tip along the string. The tester will beep every time it senses a functioning bulb.  Note where the beeping stops, then replace the previous bulb closest to the plug in.