Three problems related to wiring have been reported for the 2005 GMC Sierra 1500. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2005 GMC Sierra 1500 based on all problems reported for the 2005 Sierra 1500.
The connector that plugs into the blower motor under the glove box became too hot and melted the plastic resulting in the a/c and heat not to work (this includes the windshield defroster). I've been looking up problems and solutions and found that this is a recurring problem with GMC and chevy trucks yet there has not been any recall, in fact the dealerships have an extremely overpriced kit to fix their faulty wiring. About 66,000 mi.
Wiring harness between fan switch and fan motor get very hot at the connection and melts the connection.
Truck is now 6 years old, just over 70,000 miles. 3 to 4 years ago (maybe more) the #5 speed on the air system blower stopped working. Perhaps last summer or fall, I checked the fuses: all good. I finally found the wiring harness plug to the fan and found the #5 line had melted insulation and the surface of the contact prongs blackened. I sanded them and reinstalled the plug. All speeds worked, for a while, but soon became intermittent. Then all speeds stopped working totally. At last, I remembered that I still had an extended warranty with mastertech, checked it and was able to get the harness replaced under the warranty. The workman who did the repair said that this item was a common problem with the 2005 sierra. While I do now have a working fan control, I am afraid to use the #5 fan speed.