Why would the negative ground drain battery when car is off?

A negative ground drain does not drain the battery when the car is off. A negative ground system connects the negative terminal of the battery to the chassis or frame of the vehicle. This creates a path for the current to flow from the battery to the electrical components of the vehicle, such as the starter, lights, and ignition system. When the car is off, the circuit is broken and there is no current flowing, so the battery does not drain.

A positive ground system, on the other hand, does have the potential to drain the battery when the car is off. In a positive ground system, the positive terminal of the battery is connected to the chassis or frame of the vehicle. This means that there is a direct path for the current to flow from the battery to the electrical components of the vehicle, even when the car is off. If there is a fault in the electrical system, such as a short circuit, the current will continue to flow and the battery will drain.

Therefore, a negative ground system is preferred over a positive ground system because it does not have the potential to drain the battery when the car is off.