Final answer:
Using the vehicle's metal body as a chassis ground allows a single wire to serve as the current supply to electrical devices by completing the circuit, instead of needing two wires.
Step-by-step explanation:
In automotive electrical systems, one battery terminal is typically connected to the metal body of the vehicle, usually the negative terminal. This arrangement creates a chassis ground, where the vehicle's metal body serves as a return path for electric current. Because the metal body is a good conductor, it can effectively replace one of the conducting wires that would otherwise be needed, allowing a single wire to supply current to electrical devices. Each electrical component is connected to the battery's positive terminal through a single wire, and the circuit is completed through the vehicle's metal body back to the battery's negative terminal.