A few years ago all Christmas lights here (far up north in Europe) were in series, but today these seem to have been abandoned in favor of 12V lights in parallell with a transformer. I suppose people got tired of playing "find the broken bulb"
C-H, get a ~$1.50 series-light string, cut out one or more "12-14 volt" sections, and parallel them on the end of a cigar-lighter cord -- e.g., CalRad 90-607 http://www.ba-electronics.com/tc6111b.jpg or equal, with 3M "UG" jelly splices, and have festive dashboard lighting! ... guaranteed as distracting as any cell phone.