Thanks much for your help. After rethinking how I wanted it to operate, I ultimately spliced into the running lights wire [brown] going to the trailer connection. I connected to the lights through an illuminated waterproof toggle switch mounted behind the tailgate latching pin on the driver's side. A bed cover keeps this area dry most of the time and the switch is well protected by the tailgate when it is up or the latching pin when it is down.
