I have wired two Valks to pull trailers. Your best bet is to go with a 5 wire (what the bike has - separate brake-light and tail-light wires) to 4 wire (what almost all trailers have - brake/tail same wire) converter. I used the Hoppy 46255, which you can get at Pep Boys or on the internet (many places - many prices)
http://www.amazon.com/gp/product/B000CMKG6O?ie=UTF8&tag=googhydr-20&hvadid=4277974725&ref=pd_sl_811es8pkcv_eUsing the converter makes the whole thing much easier and the Hoppy, isolates the Valk's wiring from the trailer's so if you have some sort of the electrical problem with the trailer, it supposedly protects the bike's wiring.
I tapped into the Valk's wiring under the right side cover where the wiring harness for the rear connects. I unplugged the wires (bullet connectors) and soldered the Hoppy connections there and plugged it all back together. The Hoppy box was stored under the seat right behind the battery box in the area where it meets the rear fender. This allows access for the Hoppy's power wires to connect right up to the battery. I simply plug in the trailer pig-tail and run it down the side of the bike when I pull the trailer. It is a nice compact set up that works well.
Uhaul and a couple other places makes similar convertors/isolators, but I am not familiar with those. Hoppy makes other ones too... but for what you are doing (IF your trailer is a four wire system) you need the 46255.
