How to Use Jumper Cables on a Car | A Step-by-Step Guide

Your car won’t start. The dashboard lights dim when you turn the key. You’ve got jumper cables in the trunk. Knowing how to use jumper cables on a car is a basic skill that takes about ten minutes to master.

Before You Connect Anything

Park the vehicles close enough for the cables to reach, but never let the cars touch. Turn both engines off. Set both parking brakes and put both transmissions in Park (or Neutral for manual cars). Turn off the ignition, headlights, radio, and HVAC in both vehicles, plus aftermarket accessories like dash cams or phone chargers.

Connecting the Cables in the Right Order

The sequence matters. Follow it exactly, and verify each clamp is biting bare metal before moving to the next step.

1. Red clamp to dead battery positive. Look for the red plastic cover or the “+” symbol on the disabled battery. Attach the first red clamp there.
2. Red clamp to good battery positive. Attach the second red clamp to the “+” terminal on the donor car’s battery.
3. Black clamp to good battery negative. Attach the first black clamp to the “-” terminal on the donor battery.
4. Final black clamp to unpainted metal. On the dead car, attach the last black clamp to an unpainted bolt or the engine block, as far from the battery as possible.

That final connection is the step most people get wrong. Never attach the last black clamp to the dead battery’s negative terminal. When you complete the circuit, tiny sparks can fly. Battery gas is flammable, and a spark near the vent caps can ignite it.

The good battery should be similar in voltage to the dead one. Both should be 12-volt systems. If the donor car is running a higher-voltage system, skip the jump and call a tow truck.

Starting the Cars and Removing the Cables Safely

Start the donor car first and let it idle for a few minutes. This lets the good battery and alternator push a steady charge into the dead battery. Then start the disabled car. If it cranks slowly or doesn’t catch in about ten seconds, stop and wait a few more minutes before trying again.

Once the dead car is running, remove the cables in the exact reverse order:

1. Black clamp from the ground point on the disabled car.
2. Black clamp from the donor battery negative terminal.
3. Red clamp from the donor battery positive terminal.
4. Red clamp from the previously dead battery positive terminal.

Let the jump-started car run for at least 15 minutes before shutting it off, or drive it for a while, so the alternator can recharge the battery. If it won’t restart after a short drive, the battery may need replacement rather than just a jump.

If you’re shopping for cables for future use or need to upgrade from the cheap set in your trunk, our roundup of the best truck jumper cables compares gauge thickness and cable length so you buy a set that actually reaches in real-world parking situations.

Common Mistakes That Damage Cars

Most jump-start problems come down to a few avoidable errors. Here’s what not to do:

• Letting the vehicles touch. This can complete a circuit through both car bodies and fry electronics in either vehicle.
• Leaving anything on. Lights, radio, and accessories draw power and can cause a voltage spike when the circuit completes.
• Reversing the clamps. Red to black creates a direct short. Check every clamp before starting either car.
• Mismatched batteries. A donor battery with a much higher voltage or different chemistry can damage the dead car’s electrical components.
• Skipping the ground. Attaching the final black clamp to the dead battery’s negative post risks igniting hydrogen gas that accumulates around the battery.

Jump-starting an electric vehicle is a different procedure entirely. EVs have a standard 12-volt battery for accessories, but accessing it and jumping it safely varies by manufacturer. Some EVs have dedicated jump points under the hood; others require a tow. Check the owner’s manual before attempting any jump on an EV.