Which car battery terminal should i disconnect first

Q: What happens if you remove positive terminal first?

Its important to disconnect the negative side of the battery first, otherwise you can cause an electrical short if the positive is removed first.

Whether you need to jump start the car or it’s time to replace a battery, you must know the proper way to disconnect and reconnect the cables. Which battery cable should be removed first but installed last? If you don’t get the answer right, you could put yourself in danger.

Table of Contents Show

Identifying Battery Cables
Which Battery Cable Should Be Reconnected Last?
Why Disconnect Negative First?
Which battery terminal must be disconnected first and why?
What happens if you remove positive terminal first?
Is it OK to just disconnect the negative terminal?

In this guide, we look closer at the reasons to take the negative cable off first. We also help you identify the two battery cables and describe in-depth why this step is essential.

Identifying Battery Cables

The battery terminals in your car should be either marked or color-coded. If the terminals are marked, you will see a positive symbol on the positive terminal and a minus sign where the negative terminal is.

There’s also the chance that the caps are color-coded. In this case, red indicates a positive terminal, while the black cap shows you where the negative terminal is. If you are really lucky, your car will include symbols and colors, making it easier to identify.

The negative cable should always be removed first and reconnected last. If you take the positive off first, you could create an electrical short, and there are risks for sparks, especially if anything metal touches the area. You must take proper battery precautions to keep everyone safe.

To disconnect the battery cable, you will need a socket wrench, typically 10mm. It needs to fit on the connector bolt. Turn your wrench counter-clockwise and it should loosen. Just make sure the socket never touches both of the terminals at the same time, or you will create an electrical pathway.

When you remove the negative cable, you want to put it aside. Don’t let it touch the battery or positive terminal.

RELATED: 6 Symptoms of a Bad Ground Strap (Negative Battery Cable)

Which Battery Cable Should Be Reconnected Last?

The negative battery cable should be reconnected last and the positive cable first. When you are putting a new battery in or have finished jump starting it, you have to be careful to reconnect it appropriately. If you follow the steps you took to remove the terminals, you would simply do everything in reverse order.

With these guidelines in place, you must connect the positive terminal first. Once that is complete, you are ready to connect the negative terminal last.

RELATED: Battery Terminal Corrosion Causes (How to Fix & Prevent It)

Why Disconnect Negative First?

If you fail to remove the negative connection from the battery first, you put yourself at risk of an electrical short. As an example, if you were to drop a metal tool on the positive terminal and it also touches anything metal on the vehicle, you could create a circuit.

This problem will short your battery. It can also give you one heck of a shock. That’s why the negative cable should always be the first off and last back on.

However, it’s also just as important that the connectors don’t touch each other or anything else while you have them disconnected. Some people choose to use a plastic zip tie or another item to attach them temporarily somewhere out of the way. Just make sure you don’t let them touch anything made from metal.

Once you are ready to reinstall the connectors, you can remove them from the zip ties. Remember to install the positive cable first and always end with the negative. Give both connectors a strong wiggle to ensure that they are properly seated for the best connection.

Don’t be alarmed if you see a small spark when you put the negative cable back on. This just indicates that you re-established the electrical circuit.

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When carrying out any electrical work to your car, it is usually necessary to disconnect the battery first. This brief guide will explain the best way of going about this. Disclaimer – always check your manufacturers handbook for instructions to locate and disconnect the battery as each car differs. Rubber gloves may be handy to prevent and grease, oil or electrical sparks during this exercise. If you’re worried at all about the procedure do not hesitate to contact a car mechanic to help you.

Locate the battery

You should find the battery is a rectangular box under the bonnet of your car. However, many newer cars now have a cover for the battery (with a battery symbol on top of it) which you will have to slide off or lift up to locate the terminals. If you’re finding it difficult to locate the battery, try reading your handbook for the right location.

Recognising positive and negative/ground terminals

Next it’s a good idea to discover which terminal is positive and which is negative. The general rule of thumb is the positive terminal will have a ‘+‘ sign on it and the negative terminal will show a ‘–‘ symbol. Sometimes you may also find the positive has a red cable colour and the negative a blue colour but please double check your handbook in case this differs.

Negative first

It’s important to disconnect the negative side of the battery first, otherwise you can cause an electrical short if the positive is removed first. For instance, if you accidentally drop a spanner on the positive terminal and the spanner touches anything else that’s metal on the car you’ll create a circuit and short the battery, or even worse give yourself an electrical shock. To remove the negative cable, loosen the connector and carefully wiggle the clasp off the terminal. Next remove the positive connector in the same way. Handy tip – to prevent the connectors touching anything else on the car whilst they’re disconnected, get a plastic tie or similar and attach them to something which keeps them out of the way and not touching anything metal!

Reconnecting the car battery – positive first

Once you’re finished with the electrical work on your car, you can go ahead and replace the connectors back on to the terminals. Make sure you start the way you finished, reconnecting the positive terminal first and then the negative afterwards to prevent short circuits. Push the connector back on and give it a good wiggle to ensure you have a snug fit. Try to prevent touching any other metal work on the car with the negative connector. You may notice a small spark when reconnecting the negative terminal, but this is normal and shouldn’t be dangerous. You are simply starting the electrical circuit again in the car.

Cover the battery and close the bonnet

All that’s left now you’ve reconnected the battery is to replace any battery cover(s) you removed at the beginning and then close your bonnet. Hopefully the electrical work you’ve carried out has been a success! If you find you haven’t got any electrical power, check the terminals are clean and free from dirt and try again. Failing that, you may have shorted the battery if you touched the negative terminal on any of the car’s metal work.

If you need further advice on your car’s battery or anything electrical, MCM Garage are happy to help. Just give us a call today on 01761 415 501 or contact us via our online form and we can set-up a quick appointment.

Which battery terminal must be disconnected first and why?

Removal of Old Battery Remove the negative (-) terminal first. This precaution is necessary to avoid damage to wiring and the battery by accidentally grounding tools. Remove the positive (+) terminal.

What happens if you remove positive terminal first?

It's important to disconnect the negative side of the battery first, otherwise you can cause an electrical short if the positive is removed first.

Is it OK to just disconnect the negative terminal?

Q: Can you just disconnect the negative terminal? You can disconnect the battery's negative cable. All you are required to do is to locate the negative polarity of the battery and disconnect the terminal. Avoid the negative terminal to make contact with the positive one.