The battery ground cable connects the negative post of the battery to the vehicle frame to complete the 12-volt circuit. This cable is a heavy bundle or wires in an insulated cover or a woven web cable that has no insulation.
The web-style ground cable requires no insulation because it connects to the vehicle frame. When disconnecting the battery from the vehicle, it is safest to disconnect the ground first. If a tool inadvertently connects the cable to the vehicle, there is no discharge of power. If a metal wrench disconnecting the positive cable comes in contact with the metal of the car before the ground is disconnected, the battery can arc and cause severe damage.