Blown fuses are one of the biggest culprits of broken Christmas lights — especially if the entire chain of lights is non-functional. The good news is that they can easily be replaced!

With the plug in hand, slide the door marked "Open" in the direction pointed by the arrow.

Remove the two fuses, and inspect them by looking at them up against a bright background (such as the sky). If the fuse is good, you should see an unbroken strand of wire running between the two metal contacts.

Replace all blown fuses with new ones.