Positive or negative first when installing a car battery

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?
How to Install a Battery in Your Car
Car and Truck Battery Installation Tips

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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Read and follow the Safety and Handling Information on this website.
Clean the tray where the battery rests. Use steel wool or a wire brush to rub the metal clamps and remove any corrosion.
Place your new battery in the battery tray (make sure your battery is fully charged). Make sure it faces the proper direction so that the positive and negative terminals line up with their corresponding cables. Secure the hold-down strap in its original position over the new battery, ensuring it is properly secure to prevent movement or vibration wear. Do not tighten the hold-down bracket too hard, since this can damage the plastic case and cover.
Attach both cables. Attach the positive (red) cable first, following with the negative (black) cable.
Hand-tighten the nuts. Do not over tighten the terminal bolts; the following values are recommended:
- SAE (tapered) automotive terminal: 50 to 70 inch-lb.
- Side terminal (3/89 nut): 70 to 90 inch-lb.
- Threaded stud terminal: 120 to 180 inch-lb.

How to Install a Battery in Your Car

Learn how to install a new battery in your car.

Car and Truck Battery Installation Tips

Check mounting surface for objects or protrusions that could cause damage or wear to the case or cover. The battery must be level in the tray. Make sure there are no foreign objects in the tray that could damage the battery.
Replace cables and connectors that show signs of corrosion, rust or other damage.
Do not lift or handle the battery by its terminals.
If using a dual-terminal battery (it has both top and side terminals), use top terminals for accessory hookups and vehicle starting. Only use battery side terminals for vehicle starting.
Check for proper battery polarity with respect to vehicle specifications. “Ground” polarity is typically indicated. “Reversed” polarity can cause serious damage to your vehicle’s electrical system.
The hold-down should be tightened so that it is snug.
- Top bar or top frame hold-down: 30 to 50 inch-lb.
- Bottom recess hold-down: 60 to 80 inch-lb.
- Bottom ledge-type hold-down: 70 to 90 inch-lb.

Caution: Some vehicles equipped with advanced electrical systems may require special handling procedures. Please refer to your owner’s manual for details.