Final answer:
Neither Technician A nor B is entirely correct about automotive relays. A relay typically has at least two circuits (control and load), but there can be more. In cars, grounding the battery to the metal body allows the use of a single wire to supply current to electrical devices, as the metal body serves as the return path.
Step-by-step explanation:
Neither Technician A nor B is entirely correct. Automotive relays can contain one or more circuits. A relay usually comprises at least two circuits: a control circuit and a load circuit. The control circuit is what energizes the relay coil, activating a switch that closes or opens the load circuit, allowing current to flow (or not) to the component that needs to be powered. In some cases, a relay may have additional circuits to handle more complex control strategies, such as a dual-speed fan relay that has more than one load circuit to operate fan speeds.
In cars, one battery terminal is commonly connected to the metal body, which acts as a ground. This setup allows a single wire to supply current to electrical devices. The vehicle's metal body completes the circuit for each device back to the negative battery terminal, thus allowing the electrical system to function properly with only one wire running to each device, rather than needing a separate return wire.