GM Service Manual Online
For 1990-2009 cars only

The seat belt warning alarm (approximately one pulse per second) is activated when the following conditions are met: the ignition switch is in the ON position and the left front seat belt is unbuckled. The multifunction alarm module applies and monitors battery voltage across a fixed resistor to the seat belt switch. When the left front seat belt is unbuckled, the voltage being monitored at the multifunction alarm module is high, thus indicating that the left front seat belt is unbuckled. The alarm will sound for five seconds if the left front seat belt is not buckled when the ignition switch is turned to the ON position. If at any time while the seat belt warning alarm is sounding, the left front seat belt is fastened, the alarm will stop. The multifunction alarm module's seat belt warning alarm also incorporates an indicator within the instrument cluster. The seat belt indicator works in conjunction with the seat belt warning alarm. The indicator is supplied ignition voltage through the multifunction alarm module and junction block 2. The multifunction alarm module controls the ground path to the indicator. When the multifunction alarm module receives a signal indicating that the left front seat belt is unbuckled, it completes the ground path to the seat belt indicator. Unlike the seat belt warning alarm, the seat belt indicator will remain lit until the left front seat belt is fastened.