Connect the red cable to the positive terminal first, then the black cable to the ground
The positive terminal of your battery is marked with a plus sign (+) and is usually red. The negative terminal is marked with a minus sign (−) and is usually black. You connect the red jumper cable clamp to the positive terminal of the dead battery first, then to the positive terminal of the working battery. After that, you connect the black cable to the negative terminal of the working battery, and finally to an unpainted metal surface on the engine block or frame of the dead car — not to the negative terminal itself.
This order matters because it reduces the risk of sparks near the battery. If you reverse the order or connect both cables to the terminals, you can create a spark that might ignite battery gases. The unpainted metal ground connection on the dead car is safer than the negative terminal because it keeps the spark away from the battery acid.
Key Takeaways
- Red cable goes to the positive (+) terminal of the dead battery first, then to the positive terminal of the working battery.
- Black cable goes to the negative (−) terminal of the working battery, then to bare metal on the engine or frame of the dead car, never to its negative terminal.
- The order of connection prevents sparks near the battery, which is a safety concern because batteries release hydrogen gas.
- When disconnecting, reverse the order: remove the black cable from the dead car first, then from the working car, then the red cables.
Why the positive terminal comes first
Starting with the positive terminal establishes the main power connection. Once the red cable is attached to both positive terminals, current can flow from the working battery to the dead one. This is the connection that does the actual work of charging.
If you attached the black cable first, you would be creating a ground path before the main power path is complete. This can cause a spark when you later connect the red cable, because the sudden flow of current has nowhere stable to go. By connecting positive first, you control where the current flows and when it starts flowing.
Finding the negative terminal and the ground point
The negative terminal on the working battery is straightforward to find — it is the black or dark-colored post marked with a minus sign. Connect the black cable clamp firmly to this terminal. Make sure the clamp makes solid contact with the metal post, not just touching the plastic or rubber around it.
On the dead car, do not connect the black cable to its negative terminal. Instead, find an unpainted metal bolt, bracket, or surface on the engine block or frame. Look for something that is clearly metal and not painted over. A bolt on the engine block, the metal frame near the battery, or a grounding stud all work. Wipe away any rust or corrosion with a cloth so the clamp makes good contact. This ground connection is safer because it keeps the spark away from the battery itself.
What happens if you connect to the wrong terminals
Connecting the cables backward — red to negative and black to positive — will not start the car and can damage the alternator or other electrical parts. The current flows in the wrong direction, which the car's electrical system is not designed to handle. Some modern cars have fuses that blow to protect against this, but older vehicles may suffer permanent damage.
Connecting both black cables to the negative terminals instead of using a ground point increases the risk of a spark near the battery. Batteries release hydrogen gas, which is explosive. A spark in the wrong place can ignite this gas. While this does not happen often, it is a real hazard that the ground connection method is designed to avoid.
Disconnecting the cables in the right order
Once the dead car has started and run for a few minutes, you can remove the cables. The order of disconnection is the reverse of connection. Remove the black cable from the ground point on the dead car first. Then remove the black cable from the working car. Next, remove the red cable from the working car. Finally, remove the red cable from the dead car.
This reverse order prevents sparks and protects the alternator of the working car. If you remove the red cables first while the working car is still running, you can create a voltage spike that damages the alternator. By removing the black cables first, you break the ground path safely before breaking the main power connection.
Checking the battery terminals before you start
Before you connect any cables, look at both batteries. The terminals should be clean and free of heavy corrosion. If you see a thick white, blue, or green crust on the terminals, that is corrosion. You can clean it off with a cloth or a wire brush, or you can work around it by clamping the cable as close to the metal post as possible.
Make sure both cars are turned off before you connect the cables. On the working car, you can leave the engine off while you make all the connections. Once both cables are attached, start the working car and let it run for a minute or two before trying to start the dead car. This gives the dead battery a chance to charge slightly and makes starting easier.
Frequently Asked Questions
Can I connect both black cables to the negative terminals instead of using a ground point?
You can, and many people do without problems. However, connecting to a ground point on the engine or frame is safer because it keeps any spark away from the battery, where hydrogen gas may be present. If you do connect to the negative terminal, make sure both clamps are tight and the terminals are clean.
What if the battery terminals are corroded and I can't see the plus and minus signs?
The positive terminal is usually thicker and wider than the negative terminal. The positive cable on the car is also usually red, and the negative cable is usually black. If you are still unsure, wipe the corrosion away with a cloth or brush so you can see the markings clearly before connecting.
Do I need to remove the battery terminal covers before connecting jumper cables?
Yes, if your battery has plastic or rubber covers over the terminals, remove them first. These covers protect the terminals from accidental contact but prevent the cable clamp from making a solid connection. Once you have finished, you can put the covers back on.
How long should I let the working car run before starting the dead car?
Let the working car run for one to two minutes after you connect all the cables. This gives the dead battery a small charge and makes starting more likely. If the dead car does not start after two or three attempts, wait another minute and try again rather than draining the working battery.
Can I leave the jumper cables connected while both cars are running?
Yes, you can leave them connected while both cars run. In fact, letting them stay connected for a few minutes after the dead car starts helps charge the dead battery a bit more. Just make sure both cars are in Park or Neutral and the parking brakes are set before you leave them unattended.