Battery voltage is available at all times to the horn relay at terminals 30 and 85. When the horn switch is pressed the switch provides a ground to the horn relay coil 86. When the horn relay is energized, the relay contacts close, applying battery voltage to the horn(s). The horn(s) are grounded via CKT 150 (BLK) to ground G100 and will continue to sound until the horn button is released. The body control module (BCM) monitors CKT 28 (BLK) for a low voltage signal for approximately 3 minutes and will set diagnostic trouble code B2752 if this occurs.