Why Disconnect Negative Battery Terminal First. On most cars the earth is the negative lead. The battery terminal to be disconnected first depends on the terminal that is earthed or attached to the cars bodyWhen a car is negatively earthed then it is prudent to take off the negative terminal first and connect it last.
Ground one off first and on last for safety against shorting. Always discuss this with your dealer prior to disconnecting your battery. Unless your motorcycle is one of the very rare positive ground types this video will explain why its always better to disconnect the negative terminal wh.
Disconnecting the non-earth lead positive on most cars first is risky because of the potential for short circuits if in the process of removing the non earth terminal a tool touches both the chassis and non-earth terminal at the same time.
Then after unhooking the negative terminal and setting it aside disconnect the positive terminal. The common perception of disconnecting a battery wrong is that you will either burst into flames or fall to the ground in an electrocuted mush. If you begin to remove the positive side before the negative and your wrench would make contact with any part of the vehicle then you could cause a short in the system. A battery disconnect switch is strategically placed between the negative battery terminal and the cable.
