You can tell which bulb is out on your string of traditional Christmas lights by looking for the bulb that is “burned out” by looking at the tiny little filaments in the light bulbs to see which bulb is “burned out” or has lost it’s filament. Many times the bulb will be “smoked” as well.

How can you tell if a Christmas light fuse is blown?

The fuse is a small, glass cylinder with metal-plated ends and an internal metal filament. You can sometimes tell by sight if a fuse has blown; the metal filament inside the glass cylinder will have a break in it.

How do you find a short in Christmas lights?

Simply bring the light tester close to each bulb. The tester’s indicator will light up when it’s near a functioning bulb. If you have a non-contact voltage detector, bring the detector close to the wire section between each bulb to test for voltage. The dead section of wire will be the section after your bad bulb.

Why do Christmas lights all go out when one bulb blows?

In this setup, when a filament within any one bulb blows out, it creates an open circuit in the wiring. As we mentioned earlier, when a circuit is incomplete, or open, electricity fails to pass through any of the wire, causing all the lights to go out.

Why are there two fuses in Christmas lights?

Typically, these strings of lights have two tiny fuses, one in each side of the AC line, located inside the AC plug. The fuses are intended to melt or “blow” before the copper wires in the string could melt or cause a fire from overload.