How do you fix a half lit strand of Christmas lights?

There is either a lose or broken bulb. Check all the bulbs and if it still doesn't light, replace the string.

If you have a spare $20, this item is worth its weight in gold: https://www.amazon.com/Lightkeeper-Pro-Christmas-H...

They sell them everywhere (not just online). I was skeptical of it last year and didn't get one. This year my dad got one and i was amazed at what all it does and how well it worked.

I was mostly amazed at this:

"1). Quick Fix Piezo Trigger

For the first time this new patented technology brings you an easy-to-use system for repairing faulty bulbs. The Quick Fix Trigger sends an electrical pulse through a defective light set, repairing problems associated with defective shunts."

I dont understand it but it works and i was able to fix about 5 strings of lights using the above.

You need lots of patience for this! Plug it in, pull one bulb at a time, make sure the tiny wire is straight, and not bent, place it back in, and do the same with the rest. At times the wire will be broken off the light, so watch for that. Also use a light tester for each light one at a time. I would rather buy a set of LED's which hardly have any problems.

you are going to need an extra bulb. plug it in and from the side that is not working one by one switch the off bulbs with the good one. usually you can see which bulb is out but sometimes you can not. when you get to the bad bulb it will light up the rest of the lights when u test it with the good bulb... and it doesnt take that long but if you dont want to replace the lights then the little bit of time it will take you shouldnt be an issue:) good luck

sets of light are so inexpensive it is not worth the trouble. just replace the set with a new set.

Not worth the trouble, get a new one.