Which tool is essential for diagnosing electrical issues in vehicles?

A multimeter is essential for diagnosing electrical issues in vehicles because it measures voltage, current, and resistance, which are critical parameters in electrical systems. With a multimeter, a technician can check the battery's voltage, test various circuits for continuity, and measure resistance in components to determine if they are functioning properly. This versatility makes it an invaluable tool for troubleshooting electrical failures, ensuring that the electrical system operates efficiently and correctly.

While other tools such as wrenches, torque wrenches, and screwdrivers are important for mechanical tasks like tightening or loosening bolts and screws, they do not provide the necessary electrical measurements or diagnostics that a multimeter offers. Thus, the multimeter stands out as the key tool for anyone dealing with electrical problems in vehicles.