When disconnecting the battery cables from the battery it is important to remove the cables in a particular order to minimize the chance of personal injury and component damage. The negative (-) battery cable should be removed first to stop the body of the car from being an active ground. After the negative cable is removed and set aside, the positive cable can be removed from the battery. The cables, once removed, can be cleaned with a solution of water and baking soda to remove any corrosion.
If the positive (+) battery cable is disconnected first, the chance of grounding the positive terminal against the negatively charged car body with a wrench or other metal tool is much greater. If the battery is so grounded, the battery, alternator, ECU or other fragile electronic components may be damaged by electrical surges, or any flammable gases may be ignited by the sparks produced by the electrical arcing, leading to possible fatal personal injury.
The battery cables should also not be disconnected with the ignition in the ON position. The sudden removal of the electric current can cause numerous electrical surges throughout the electrical system. These surges can damage any of the various voltage sensitive components such as the ECU. Always make certain that the ignition switch is turned OFF .