Which of the following is NOT a common source of accidental vehicle fires?

The choice of a carpeted floor as not being a common source of accidental vehicle fires is accurate because while a carpeted floor might be flammable, it typically does not initiate a fire on its own. In contrast, the other options represent more direct and common causes of vehicle fires.

Electrical system failure can lead to shorts or sparks that ignite flammable materials, such as gasoline or upholstery, making it a well-known cause of vehicle fires. Spilled fuel or oil presents an immediate risk, as these substances are highly combustible and can easily catch fire, especially if they come into contact with a hot engine or exhaust system. Overheating engines can also ignite nearby materials or cause fluids to vaporize, creating highly flammable conditions.

Thus, the carpeted floor is less likely to be a primary source of accidental fires compared to the other options, which are well-documented risks associated with vehicle fires.