Connect the red cable to the dead battery first, then to the good battery

Jumper cables transfer power from a working battery to a dead one through a direct electrical connection. The process takes about five minutes and requires two batteries, two sets of cable clamps, and a working vehicle. The order matters: you always connect to the dead battery before the good one, and you always disconnect from the good battery before the dead one. This prevents sparks near the dead battery, where hydrogen gas may be present.

Before you start, make sure both vehicles are parked close enough that the cables will reach between the batteries without stretching. Turn off both engines. Open both hoods and locate the batteries — they are usually under the hood on one side, typically marked with a red positive terminal and a black negative terminal. If either battery is cracked, leaking, or visibly damaged, do not attempt to jump it. Call a tow truck instead.

Key Takeaways

  • Always connect the red clamp to the positive terminal of the dead battery first, then to the positive terminal of the good battery.
  • Connect the black clamp to the negative terminal of the good battery, then to an unpainted metal surface on the dead car's engine — not directly to the negative terminal.
  • Start the working vehicle and let it run for two to three minutes before starting the dead car.
  • After both engines are running, wait five minutes before disconnecting, and remove cables in reverse order: good battery negative, dead battery negative, good battery positive, dead battery positive.

Step 1: Attach the red cable to the dead battery's positive terminal

The positive terminal is marked with a plus sign or the letter P, and is usually red or has a red plastic cover. Clamp the red cable's clamp firmly onto this terminal. You should hear or feel a click, and the clamp should not slide around when you tug it gently. A loose connection will not transfer power.

If the terminal is corroded (covered in white, blue, or green crusty buildup), scrape it clean with a wire brush or the edge of a coin before clamping. Corrosion blocks the electrical connection. Wipe away the debris with a dry cloth so you can see bare metal underneath.

Step 2: Attach 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. Again, make sure the clamp is tight and does not move when pulled. This completes the positive circuit between the two batteries.

At this point, you have one complete red cable running from the dead battery to the good battery. Do not start either engine yet — wait until the black cable is also connected.

Step 3: Attach the black cable to the good battery's negative terminal

The negative terminal is marked with a minus sign or the letter N, and is usually black or has a black plastic cover. Clamp the black cable to this terminal on the working battery only. Do not attach it to the dead battery yet. Make sure the clamp is tight.

At this point you have the red cable fully connected between both batteries, and the black cable connected to only the good battery. The final connection — from the black cable to the dead car — comes next.

Step 4: Attach the black cable to the dead car's engine, not the battery

This is the step most people get wrong. Take the other end of the black cable and clamp it to an unpainted metal surface on the engine of the dead car — a bolt, a bracket, or a clean spot on the engine block itself. Do not clamp it to the negative terminal of the dead battery. Connecting to the engine instead of the negative terminal reduces the risk of sparks igniting hydrogen gas that may be present around the battery.

Choose a spot that is clearly metal and not painted, plastic, or rubber. If you are unsure, ask the owner of the dead car or consult the owner's manual. A good target is often a bolt on the engine block, a bracket holding the alternator, or the metal frame of the engine itself. Wipe away any dirt or corrosion from the spot before clamping.

Step 5: Start the working vehicle and wait

Start the engine of the car with the good battery. Let it run for two to three minutes. This gives the dead battery time to charge and builds up enough power to start the other engine. You should not rev the engine or press the accelerator — just let it idle at normal speed.

During this time, listen for any unusual sounds or smells. If you hear crackling, smell burning plastic, or see smoke, stop when ready and disconnect the cables. These are signs of a serious problem.

Step 6: Start the dead car

After two to three minutes, try to start the dead car. Turn the key or press the start button as you normally would. If the engine does not turn over after five to ten seconds of cranking, stop and wait another minute. Trying repeatedly drains both batteries and can damage the starter motor.

If the car still will not start after a second attempt, the battery may be too dead to jump, or the problem may not be the battery at all. Stop and consider calling a tow truck or a roadside service. Continuing to crank the engine will only make things worse.

Step 7: Disconnect the cables in reverse order

Once both engines are running, wait at least five minutes before disconnecting anything. This gives the dead battery time to recharge. Then remove the cables in this exact order: black clamp from the dead car's engine, black clamp from the good battery, red clamp from the good battery, red clamp from the dead battery. This reverse order prevents sparks and protects both electrical systems.

After disconnecting, keep both engines running for at least five more minutes. The dead car's alternator will continue charging the battery. If you turn it off when ready, it may not start again. Once you are confident the dead car is running smoothly, you can turn off the working vehicle.

What to do after the jump

Drive the car that was jumped for at least 20 to 30 minutes so the alternator can fully recharge the battery. Highway driving is better than stop-and-go city driving for charging. Avoid turning off the engine and restarting it right away, since the battery may not have enough power yet.

If the car starts and runs normally, the battery was likely just drained and is now recovering. However, if the car dies again within a few days or weeks, the battery may be failing and will need to be replaced. A battery that dies repeatedly is no longer holding a charge and cannot be revived by jumping.

Frequently Asked Questions

What if the battery terminals are corroded and I can't get the clamp to grip?

Use a wire brush, a coin, or a small knife to scrape away the white, blue, or green buildup until you see bare metal. Wipe away the debris with a dry cloth. Then try clamping again. Corrosion is a common reason jumper cables do not work, and cleaning it away usually solves the problem.

Can I connect the black cable directly to the negative terminal of the dead battery?

Technically yes, but it is not recommended. Connecting to an unpainted metal surface on the engine is safer because it reduces the chance of sparks igniting hydrogen gas that may be present around the battery. If you must connect to the negative terminal, make sure the battery is not cracked and is not leaking fluid.

How long should I let the good car run before trying to start the dead car?

Two to three minutes is usually enough. If the dead battery is very old or very dead, waiting five minutes is safer. There is no harm in waiting longer, but you do not need to wait more than ten minutes.

What if the car still won't start after I jump it?

The battery may be too damaged to hold a charge, or the problem may be something else entirely — a bad starter, a fuel pump, or a corroded connection elsewhere. If jumping does not work after two attempts, the car needs professional diagnosis and should not be jumped again.

Do I need to drive the car after jumping it?

Yes. Drive it for at least 20 to 30 minutes so the alternator can recharge the battery. If you turn it off right away, the battery may not have enough power to start it again. Highway driving is better than stop-and-go city driving for charging.