Should the car power disconnect switch cut off the positive or negative terminal?

[JaceRose]

To save space, cars generally use a single-wire system where the negative terminal of the battery is directly connected to the vehicle frame. The negative terminals of onboard electrical devices can simply be connected to the nearest point on the vehicle body. Therefore, when disconnecting power, it's sufficient to remove the negative terminal of the battery, which prevents accidental short-circuiting. Below are relevant explanations: 1. Negative terminal: The negative terminal of a car battery is connected to the vehicle body, meaning the entire car body serves as the negative terminal. This allows any electrical component's negative terminal to be grounded by simply connecting to the vehicle body, as the current will return to the negative terminal through the body. This eliminates the need to run separate wires from each component to the negative terminal, significantly reducing wire usage and simplifying circuit fault diagnosis. 2. Positive terminal: If the positive terminal is disconnected instead, since wrenches are metal and conductive, accidentally touching any metal part of the vehicle body during removal would directly connect the battery's positive terminal to the negative terminal, causing a short circuit.