The battery voltage is available at all times to the horn relay at terminal 1 and terminal 3. The horn switch provides a ground to the horn relay coil when the horn switch is pressed. The relay contacts close and apply battery voltage to the horns when the horn relay is energized. The horn continues to sound until the horn switch is released. The body control module (BCM) also has the ability to sound the horns by supplying a ground for the horn relay via CKT 28.