0kelseymh 8 years ago ReplyUpvoteI guess that you've got several strings of old-school "flashing" Christmas lights. The first thing to do is to remove the magic bulb (it usually has a red-painted tip) that causes the flashing, and replace it with a regular bulb. Do this in all of your strings. Now all of your lights are "synchronized", in the sense that they are on all the time.If all the strings are plugged in series, or at least into a single power-strip/extension-cord/horrifying-tree-of-adapters, then you can put a single flasher unit between your strings and the wall plug. There's an Instructable for this, or you could buy one, or you could try a Google search (fiddle with the keywords to get better results).