NO TAIL LIGHTS

I had a blown fuse on my 2004 Itasca Sundancer, I had the problem with no marker lights & tail lights. I separated the rear pigtail then the marker lights would stay on, but once I reconnect pigtail with tail lights, it blows a fuse. I have it narrowed down to the tail lights I think. The tail lights are Peterson 426 sealed lights. They do work with brakes and blinkers but no tail lights. Any ideas where to go next??