One problem related to wiring has been reported for the 2004 GMC Sierra. The most recently reported issues are listed below.
The windshield is leaking water down into the electrical system. The wiring is shorting out. Also, the linkage has fallen out. You can smell burnt wiring and smoke. The consumer has contacted the dealer several times. The dealer continuously told the consumer that the gentleman was not there that she needed to see. Consumer had someone else look at the vehicle. And was told the vibration from driving had jarred the the pin loose. The blower, heat, and the transmission failed.