Final answer:
Technician B is correct. For accurate voltage measurements with a scope meter, connect one lead to the alternator's output and the other lead to a ground. This setup aligns with standard voltmeter use and the vehicle's common ground system.
Step-by-step explanation:
The correct connection of a scope meter or any voltmeter in a vehicle when measuring voltage output is a crucial aspect to ensure accurate readings and safety. Technicians A and B are discussing the proper way to connect a scope meter to measure voltage output at the alternator. Technician B is correct; you should connect one lead of the scope meter to the alternator output terminal (positive) and the other lead to the ground (negative). This allows the scope meter to measure the potential difference between the alternator's output and the ground, giving an accurate representation of the alternator's voltage output.
This method is in line with how voltmeters are typically used to measure voltage across a component: they are connected in parallel with the component - one lead to the positive side and one lead to the negative side. Moreover, when we consider how a car's electrical system is set up, with one battery terminal connected to the metal body, it creates a common ground system that allows current to return through the vehicle's chassis. Therefore, by connecting the negative lead to the chassis or a ground point in the vehicle, you are completing the circuit needed for the voltmeter to function.