The GMC window regulator is made up of at least two dozen parts, all of them under stress from the effects of heat and cold, moisture and dirt. Eventually, the loss of lubrication and the constant use will mean that one of the parts will give way. When that happens, the motor and fuses that power the window might fail as well. If your window is starting to resist opening or closing, or refuses to budge, you first must diagnose whether the issue is mechanical or electrical. To determine if the motor is at fault, listen for any noise when you press the window switch. If there is just silence, it is more likely that the switch, wiring, fuses or motor are the problem. But, if you hear the sound of whirring or grinding, the issue is probably your GMC window regulator. To pinpoint the problem with the electrical door system, visually inspect the fuses and wiring for signs that the system had blown. Consult your GMC owner's manual and study the wiring diagram, then use a 12-volt test light to check the circuits. Once you have decided that your GMC window regulator is at fault, then order your new regulator set here. Because of the labor that it requires to open a door panel and take it apart, it is more sensible to replace the entire regulator set at once.