im assuming then that youre talking about the 7 pin rather than a 4 pin... If i remember correctly one of them is +12v all the time. Its to charge AUX things... maybe your plug is wired wrong, or the trailer is wired wrong. I would verify your truck because its more important that that is correct rather than the trailers... otherwise you'll have issues with most trailers. http://www.chuckschevytruckpages.com/images/7pintrailer.jpg might help you trace it.