If an entire set of mini lights has gone out, more than likely, you've blown a fuse. This commonly happens when too many mini lights sets are connected in series.

In most sets of Christmas lights, there are one or two fuses located in the male plug. If too many sets are connected in series, they will draw more current than they can handle safely, and the fuses will "blow." Unplugging the sets and replacing the fuses should restore them.

Replacement fuses are usually packaged with replacement bulbs in tiny little bags and taped to the Christmas light strings near the male plug. Be sure to collect these little bags into labeled bags for the future.

Using a small short flathead screwdriver, slide back a little door on the male plug and use a small flathead screwdriver - the kind used to open little screws on battery doors - to gently pry out the burned-out fuse and gingerly install a new fuse.

If replacing the fuse does not solve the "lights-out" issue, an alternative issue might be an unseated bulb. So, if your fuses are OK, look for a damaged bulb base or unseated bulb. If a bulb is damaged, use one of the included extra bulbs as a replacement.

See the links to videos about changing fuses in Christmas lights below.

If all of a set of Christmas lights has gone out, more than likely, a fuse has blown. If just a few lights are out, the issue is not the fuse. To confirm if the fuse is blown, open up the fuse compartment door in the male plug of the light string, remove the fuse with a small flathead screwdriver and see if the hair-thin fuse wire is broken. The fuse may have a dark residue inside the glass if the fuse is blown.

Fuses in Christmas lights blow when too many sets of lights are connected end-to-end. Fuse blow to protect users from plugging too many light sets together and creating an electrical hazard. After replacing the fuse, plug together only the maximum number of light strings or less than is indicated in the light set's specifications.

Remove both fuses. Look for metal contacts at each end of both fuses. If there are two sets of contacts, both fuses are required. If one fuse has no metal contacts in the fuse compartment of the male plug then it is an extra replacement fuse.

Most (but not all) Christmas lights have a fuse or set of fuses installed in the mail plug. Slide back a little door using a small flathead screwdriver into a slot or depression. Some male plugs will have a screw-out fuse assembly between the prongs. Using a small screwdriver to unscrew the assembly and replace the fuse.