|Lightkeeper pro was very easy to use to fix.|
Incandescent Christmas lights
1. Remove 1 miniature bulb (with the lights plugged in).
2. Plug the tester in where you removed the light bulb.
3. Pull the trigger a few times (In most cases the section lit on the first pull).
4. Replace the bulb.
This will be especially helpful on prelit Christmas trees or Christmas lights that go out once there on the tree. This product really is true genius. This was the best money I've spent in a long time. It literally saved me about 3 hours of playing with bulbs.
There are other functions on the tester -tool to easily pull bulbs, non-touch tester to find a loose bulb, built in light to see what your doing, and replaceable batteries (3 button cells). I used the additional features to find light strands that were missing a bulb or other weird stuff.
If you really want to know how it works (the physics geek in me), the full explanation on How the Lightkeeper Pro works from them.
Here's a link to the LightKeeper Pro on Amazon:
Target, Wallmart, and Menards also have it, but I couldn't find it on their websites... Stop throwing out the Christmas lights strands just because you can't get them to work. For under $20 troubleshoot and fix them in a few minutes, then you can enjoy the holidays.