Have couple box of Christmas lights.
All were tested and most or all of the bulbs lite up. Both boxes have several new strings.
One string did not light and I got it mixed up with the others in the second box.
Maybe a blown fuse.
The first box has 10 strings of various lengths and a box of extra bulbs and fuses.
The second box has 17 strings at least 16 which work and some extra bulbs and fuses.