Connect the red cable to the dead battery's positive terminal first
The correct order matters because it prevents sparks near the battery. Start by opening both car hoods and locating the battery terminals — the positive terminal is marked with a plus sign (+) or a red plastic cover, and the negative terminal is marked with a minus sign (−) or a black plastic cover. Clamp the red cable's first clamp firmly onto the positive terminal of the dead battery. You should hear or feel a solid click when the clamp is seated properly.
Do not let the metal clamps touch each other or any other metal part of the car while you work. If the battery terminals are corroded with white, blue, or green buildup, use a wire brush or old toothbrush to scrub them clean before clamping. A loose connection will prevent current from flowing and the jump will fail.
Connect the red cable to the good battery's positive terminal
Take the other end of the red cable and clamp it to the positive terminal of the working battery in the other vehicle. Again, make sure the clamp is tight and fully seated. At this point you have a complete circuit for positive current between the two batteries.
The red cable now carries current from the good battery to the dead one. Keep your hands and any metal tools away from both clamps while this connection is live, even though the circuit is not yet complete.
Connect the black cable to the good battery's negative terminal
Take the black cable and clamp its first end to the negative terminal of the working battery. This is the critical step that prevents sparks: by connecting the negative to the good battery first, you avoid creating a spark near the dead battery, where hydrogen gas may be present.
Make sure this clamp is also tight and fully seated. The black cable will now be ready to complete the circuit, but the spark risk stays away from the dead battery itself.
Connect the black cable to an unpainted metal surface on the dead car
Do not clamp the black cable directly to the negative terminal of the dead battery. Instead, find an unpainted metal bolt, bracket, or engine block surface on the dead car — somewhere at least 12 inches away from the battery itself. Clamp the black cable there. This final connection completes the circuit while keeping any spark away from the battery terminals.
If you cannot find an unpainted surface, scrape away a small area of paint with a screwdriver or knife to expose bare metal, then clamp there. The connection must be metal-to-metal to work. Once this clamp is seated, both vehicles are now connected and current can flow.
Key Takeaways
- Connect red to the dead battery's positive terminal first, then red to the good battery's positive terminal.
- Connect black to the good battery's negative terminal, then black to an unpainted metal surface on the dead car — never directly to the dead battery's negative terminal.
- Clean corroded terminals with a wire brush before clamping to may support a solid connection.
- Keep the metal clamps from touching each other or any other metal while you work to prevent accidental sparks.
- Start the working vehicle first, wait two to three minutes, then start the dead vehicle.
Why the order and placement matter
Car batteries produce hydrogen gas, especially when they are deeply discharged or being charged. A spark near the battery terminals can ignite that gas and cause an explosion. By connecting the negative cable last and placing it away from the battery, you move any spark risk away from the source of the gas.
The positive-to-positive connection first ensures that current can flow before you complete the negative circuit. If you reversed the order and connected negative first, you would create a spark at the positive terminal when you clamp the red cable, which is exactly what you are trying to avoid.
Disconnecting the cables in the right order
Once both vehicles have run for several minutes and the dead battery has recharged, remove the cables in reverse order. Start by unclamping the black cable from the unpainted metal surface on the dead car. Then unclamp the black cable from the good battery's negative terminal. Next, unclamp the red cable from the good battery's positive terminal. Finally, unclamp the red cable from the dead battery's positive terminal.
This reverse sequence prevents a spark at the moment of final disconnection. Leave the revived vehicle running for at least 20 minutes to allow the alternator to recharge the battery fully before turning it off.
When not to jump a battery
Do not attempt a jump if the battery case is cracked, leaking, or visibly damaged. Do not jump if the terminals are so corroded that you cannot clean them, or if the battery smells like rotten eggs or sulfur — that smell indicates internal damage. Do not jump if the battery is frozen or if you see ice on or around it.
If the vehicle has a modern computer system or expensive electronics, consult the owner's manual before jumping. Some vehicles require the negative terminal to be disconnected before any jump attempt, and some have a specific grounding point you must use instead of the engine block.
Frequently Asked Questions
What if I connect the cables in the wrong order?
If you connect black to the dead battery first, you risk creating a spark near the battery terminals where hydrogen gas may be present. Stop when ready, unclamp the cables in reverse order, and start over with the correct sequence. Do not proceed if you smell gas or see any smoke.
Can I clamp the black cable directly to the dead battery's negative terminal?
You can, but it is not safe. Clamping to an unpainted metal surface away from the battery moves the spark risk away from the hydrogen gas. If you must clamp to the negative terminal, do so only as a last resort and be prepared for a possible spark.
How long should I wait before starting the dead vehicle?
Start the working vehicle first and let it run for two to three minutes. This gives the alternator time to begin charging the dead battery. Then start the dead vehicle. If it does not start after 30 seconds of cranking, wait another minute and try again rather than draining the good battery.
Do I need to remove the negative terminal from my car before jumping?
Most modern vehicles do not require this, but some do — especially those with sensitive computer systems. Check your owner's manual before jumping. If the manual specifies a grounding point or a different procedure, follow that instead of the standard method.
What should I do if the battery still will not start after jumping?
Leave both vehicles connected and running for five to ten minutes, then try again. If the vehicle still does not start, the battery may be damaged beyond recovery, or the problem may be something other than a dead battery — such as a bad starter or alternator. Disconnect the cables and have the battery tested by a technician.