Or none of them work because of one bulb. But you don't know which one. Because none of them work.
Christmas lights are 1.5 volts each. Or 3 volts, I don't remember.
My dad & I used to chop up Christmas light strands & wire little groups of them together in series so they'd run on those little flat Polaroid camera batteries, using paper clips as the electrodes, and hang them on a kite line, a few feet below the kite.
(if you attach them to the kite itself, it screws with the balance & it doesn't fly right.)
Back in the mid 1980's, one night the wind was blowing south, over the neighborhood, and my dad was at the park with the kite. I was riding my bicycle around the neighborhood watching the lights from different perspectives. I was 6 or 7 years old.
One of the blue lights fell off the kite line and landed on an old man's front porch, still lit. So I ran up & grabbed it.
The old man called the police because he thought it was a UFO.
When I picked it up and ran back to my bike with it, he didn't see me through the living room curtains but he saw the blue light. He told the cops this UFO crashed on his porch and then got up and flew sideways about 3 feet off the ground, then flew up the street and around the corner.
My dad's friend Louis who was a teenager at the time, was with us at the park and my dad had sent him to come find me.
Louis found me & I told him about the lights landing on Old Man Johnson's porch.
We went back and my dad had wound up the kite because he saw it fall off & didn't want to lose any more.
On the way home, we saw cops enter the neighborhood and stop at Old Man Johnson's house.
We went over there and Mr Johnson waved us over, to ask if we saw the UFO.
My dad told me not to say anything, but Louis backed up the old man's story & said he also saw it flying around the neighborhood and had stopped to get my dad and the 3 of us were out on bicycles trying to find the aliens or their mother ship.
Later my dad asked Louis why he did that & he said it's because he didn't want Old Man Johnson to look like a senile old fool in front of his wife and his neighbors.
Mr Johnson was a friendly old man who used to ride his bicycle around the neighborhood with his dogs on leashes & everybody knew him. He's in the background with his dogs going past in a picture of my sister at the bus stop on her first day of school which I think was 1981.