Ya know when you open up a brand new set of christmas lights, and they come with that little bag of replacement bulbs? KEEP THEM! They saved me 50 bucks this year ALONE! I use these for making a normal christmas light sets flash on and off. The best part though is that all you need is the replacment bulb bag (and its contents) from a random flashing icicle set.
Step 1: This might be all you have to do!
This step can either be the first, or last depending on you light sets. If you are lucky all you have to do is pull out the entire bulb and replace it with a "replacment bulb" from your twinkling light set, and make sure it has to red tip and a wierd looking filament. It usually takes 2 flashing bulbs to get string of lights to work completely