I did this mod awhile back and used the adapter it is listed in the classifieds. http://www.venturerider.org/forum/photopost/showproduct.php?product=4&title=aux-lighting-harness-for-2nd-gen-venture&cat=18
I liked the way you ran the wires in the bag rails, I was lazy and just used snakeskin and tied wrapped the wires to the rails.