how to fix christmas lights half out without a tester

If you don't have a tester, you can check the fuse to see if it is blown. If it is, then you'll need to replace the fuse. If not, then you'll need to check the wires and make sure they're not damaged or loose. Make sure to check the entire string of lights before replacing any wires or fuses. If everything looks good and it still doesn't work, then you may need to replace the entire set of lights.