The wiring schematic is the cornerstone of electrical diagnosis. Schematics break the entire electrical system into individual circuits, showing the electrical current paths when a circuit is operating properly. Wiring which is not part of the circuit of interest is referenced to another page, where the circuit is shown complete. Schematics use a top (power) to bottom (ground) sequence to present electrical information.

Important: The schematic does not represent the components and wiring as they physically appear on the vehicle. For example, a 4-foot length of wire is treated no differently in a schematic from one which is only a few inches long.

When diagnosing a horn problem, reference the horn section. The following schematic is a typical example of a schematic with its supporting text.

Battery voltage is applied to the horn relay at all times on circuit 439 (ORN). When the horn switch is pressed the relay coil is grounded through circuit 28 (BLK) and the relay energizes. When the relay energizes the contacts closes and both the LH and RH horns sound.