One problem related to wiring has been reported for the 2009 GMC Sierra. The most recently reported issues are listed below.
2009 GMC Sierra had a incorrect marked wire for the trailer power. The consumer stated when connecting the trailer power, he connected the wire at the fuse panel marked trailer power feed. When there was no power at the trailer connection he contacted the dealer. They determined that the wire marked trailer power feed was not the trailer power feed wire. They disconnected the wire and connected a different wire which did in fact supply power to the trailer connection.