Replace all nonfunctioning bulbs.
Easy way to check christmas light bulbs.
The easiest way to find faulty bulbs on incandescent christmas lights is with a christmas light tester.
Simply bring the light tester close to each bulb.
Light testers search for the point in the string where the voltage changes between a good bulb with current flowing and a problem area with minimal current.
Use a light tester to test each bulb individually.
Most lights are now wired so that if one is out the rest burn.
The only way i know how to do what you want is to take a bulb you know burns and replace each bulb in the string with that bulb until they all glow.
Step 2 locate the two wires on the bottom of the bulb and touch a probe to each wire ensuring that the probes do not touch each other or more than one wire.
Begin at one end of the darkened string of christmas lights and carefully remove the first bulb.
Sometimes nonfunctioning christmas light bulbs can appear to be perfectly normal so a light tester is the most efficient and reliable way to single out broken bulbs.
Reinstall it and see if it works.
Second test the christmas light bulbs with an inexpensive tester available where holiday lights are sold and online usually changing a problem bulb or tightening it will fix the entire strand.
The christmas light tester will indicate which bulbs are bad and need to be replaced.
Sometimes it does but usually it doesn t.
The tester s indicator will light up when it s near a functioning bulb.
If you re able to locate a bad bulb just unseat the bulb remove the bulb from the plastic base and replace it with a similar bulb.
Easy way how to fix christmas lights finding bad bulb locating lamp repairing fixing christmas tree string of lights that are not working how to locate what light bulb is bad how to find what bulb is blown just get ideal volt tester detector probe sensor fixing string of christmas lights ideal volt sensor.
Some christmas light testers work by having you slide each christmas light bulb through a hole.