Repairing Christmas tree lights can be a simple process if you know what to look for. The most common issue is a bulb that has burned out, which can be easily replaced by finding the faulty bulb and replacing it with a new one. If the entire strand of lights is not working, it could be due to a faulty connection or a blown fuse. First, try checking the connections to make sure they are secure and tight. If the problem persists, you may need to replace the fuse. If neither of these solutions work, the lights may be damaged beyond repair and will need to be replaced.