Which Terminal to Disconnect First on a Car Battery?

When you start to get problems with your car, you may want to try and diagnose or fix something on your own. One of the first things you will have to learn is how to replace and disconnect the battery, with many people unsure which terminals to disconnect first.  

To safely disconnect from the terminals on your car battery, remove the negative, black cable first while ensuring the car key is not inserted. It is important to ensure that the car is not currently running and that you do not directly touch the terminals while disconnecting.  

We always recommend when you are removing a battery, you understand how everything works and how to do it properly to ensure that nothing is broken. Many people have made the mistake of connecting and disconnecting cables to cause the car to burn completely.  

Pro Tip: If your car battery is dead, don’t throw it away! Check out this tutorial on how to bring your dead battery back to life and save a lot of money! This little known method is simple, quick and works for almost ANY battery out there!

Does It Matter Which Battery Terminal You Disconnect First? 

Disconnecting the right battery terminal is important to ensure that your car stays safe and that nothing goes wrong during the process. If you disconnect the wrong terminal first, there is a much higher chance that something can go wrong, and the car will experience a sudden surge in power.  

Many owners have thought that changing the battery is just unscrewing and unbolting everything and popping in a new battery. The best-case scenario is that a few fuses have been blown, and the new battery is connected to the car, requiring only a few easy-to-find parts to fix the car.  

Whereas the worst-case scenario is that the internal wires of the car spark thanks to the arcing, and a fire suddenly starts. This will cause issues, as car fires start quickly and, once started, are nearly impossible to stop, leaving you with much less than a car that won’t start.  

Why Not to Disconnect The Live Cable First? 

You should not connect the live or red cable from the terminals first because this can be considered the main point where power comes from. But, disconnecting it first will cause arcing and surges to go through the car damaging the battery and internal wires.  

Many people assume that it does not matter which cable you disconnect, which is not true as electricity is always willing to make life difficult. You must ensure that the black wire, the negative terminal, is disconnected first, as the battery will not want to arc towards it.  

It should be noted that there will still be a few sparks, especially if you aren’t careful when disconnecting it, but it will not arc. The negative terminals of the battery cannot cause a surge to happen to the battery or for a surge to arc into the electric systems of the car.  

How Do You Know Which Cables Are Live And Negative?

Now that you know what cable to disconnect first, we need to ensure that you can easily recognize what cables are negative and live. People who have not worked on electrical systems before may not easily recognize which cables go where or what color coding means.  

There are only two cables that will ever connect to the terminals on your car battery; if there are more, then it will be something that has been added by someone else. Car manufacturers worldwide have standardized the cable colors in all cars; even modern electric cars that do use normal car batteries have the same color coding. 

The Red Cable 

The red cables in your car will always be the live wire; this is the entryway for electricity into the car’s systems. These cables will be disconnected last when connecting a new battery and must be connected first when connecting the new battery to your car.  

If you are working on the deeper cables within your car, you will need to use a wiring map to ensure that the cables are what you expect them to be. The cables can become extremely complicated inside your car, especially when someone has already tried adding new accessories.  

The Black Cable 

The black cable will always be the negative cable going to your battery; this is the cable that you should disconnect first. These cables are technically safe to touch with your bare hands as long as you are not grounded, but we never recommend doing this just out of safety concerns.  

Unlike the live wire, many black cables run throughout your car, so knowing their purpose means using a wire map. When jumpstarting your car, we recommend connecting the black wire to a bare piece of metal and not the black terminal on your car.  

Can You Disconnect Battery Terminals While The Car Is Running? 

It is extremely dangerous to disconnect your car’s battery terminals while running because of the danger of shorting the battery and the live wires. When the engine is still running, there is still a lot of electricity being produced from the engine.  

The alternator is attempting to recharge the battery, which means the power is still running through the cables that are now hanging loosely. Not only can this cause a short, but the wires can touch you and cause dangerous amounts of electricity to flow through you.  

Further, many modern cars require some power from the battery, which means that the engine may stop as soon as the battery is removed. This will damage your car’s internal systems and cause almost irreparable damage to parts of the car that can cost thousands to fix.  

Which Terminal Should You Connect First When Reconnecting The Car Battery? 

When reconnecting the battery, after having it charged, or when the new one has been installed, you need to follow the same steps in reverse. Connect the live wire, red, first, and then connect the negative wire, securing both using the bolts that should be connected to the cables.  

We always recommend that you follow this order of operations to ensure the battery is not damaged and prevent surges into the car. Many times, the same place where you are buying your battery will also be willing to install it without any extra charges.  

Having someone install your new battery for you will ensure that it is done properly and that the old used-up battery can be disposed of properly. You cannot leave a dead batter in the corner of your garage or shed and hope that nothing ever happens as it will eventually start to leak.