Get the wiring harness adapter from M61A1MECH it will make it much easier to connect your trailer adapter. I use the Hoppy isolated adapter from Autozone I think it's around 45 to 50 bucks and it draws the power from your battery so if you get a short in your trailer the bike lights still work.
Here is the link to the harness adapter.
http://www.venturerider.org/classifieds/showproduct.php?product=4200&title=auxillary-tail-light-harness-for-royal-star-venture&cat=35
Adapter
http://www.autozone.com/autozone/parts/Hopkins-Trailer-Tail-Light-Converter/_/N-a8pa0?itemIdentifier=70605_534335_0_