Jumper Cables

jumper cables

Your car battery could be too weak to start your car for a number of reasons: faulty alternator, lights left on, cold weather, or simply an older battery that is no longer holding an adequate charge. Whatever the reason, you can use a jumper cable to connect your dead battery to a full vehicle battery of the same size. The full battery then charges your dead battery enough to start your car again.

Park the donor vehicle (with the full battery) next to the vehicle with the dead battery.

Place the vehicles so that the batteries are as close together as possible, but make sure the two cars are not touching.

Turn off the radio, headlights, and interior lights, and if safe to do so, turn off the hazard lights on both vehicles.

Shut off the engines of both vehicles.

Apply the handbrakes and shift into the park (automatic transmission) or out of gear (manual transmission).

Identify the positive and negative terminals of the batteries.

The wires going to the positive battery terminal are almost always red. In case of doubt, the battery itself has a plus (“+”) and a minus sign (“-“), which indicate the plus and minus pole. Check the battery terminals for rust before you start the jumper. Clean them if you notice rust on the poles. Then try to start the car again before continuing with the lockup. The battery may not be dead, it was just badly connected.

Keep the jumper wire terminals separate so there is no risk of them accidentally touching each other — this could cause a short circuit.

The wires in jumper cables are usually not the same length to avoid touching each other. If they’re the same length, you want to make sure they haven’t been altered or damaged.

Clamp one of the red clamps firmly to the positive post of the dead battery.

Make sure the clamp is firmly attached to the battery post. On some vehicles, you will need to remove a plastic cover from the battery’s positive terminal before you can make this connection.

Attach the other red clip to the positive terminal of the donor battery.

Again, make sure the clamp is securely fastened and will not slip off due to vibration in the engine bay.

Connect one of the black jumper wire clips to the donor battery negative terminal.

Earth the last clamp.

Attach the other black clip to an unpainted metal surface inside the engine compartment of the vehicle with the dead battery – the further away from the battery the better. An unpainted bolt on the engine block would be ideal. Remember that the clamp can “bite” firmly on the object in question and must hold firmly, even if the motor vibrates. You can theoretically connect the second black clamp to the negative pole of the dead battery instead. However, this creates a spark that could ignite hydrogen vapor from the battery. Check that no part of the jumper cables — or tools or battery covers — are dangling into the engine compartment where they could hit belts, pulleys, or other moving parts.

Start the donor vehicle and let it idle for a few minutes before attempting to start the car with the dead battery.

If you’re trying to start the car with the dead battery, rev the engine to around 3,000 pmz.

Once you get the car running with the dead battery, disconnect the jumper cables in the following order:

Negative ground (engine block or, less desirable, dead battery negative). Negative pole (black clip) on the donor battery. Positive pole on the donor battery. Positive pole on the previously empty battery.


Don’t turn off the car you just jump-started until you’re in a safe place or have another bypass handy. Depending on the condition of your battery and your alternator charging the battery, you may need to jump-start the car again. Leave the just jump-started car on for at least 15 minutes to allow the alternator to charge the battery. Some vehicles have a plastic cover over the entire battery. You must remove these before you can jump-start the car or use it to jump-start other vehicles. The cover usually comes off easily with hand screws or a simple screwdriver. Check under your hood before the problem arises to make sure you have a screwdriver or other tool with you in case of need. Some vehicles have the battery under the back seat or in the trunk, but there is always a jumper connector under the hood. It is marked with a red plastic cover with a plus sign on it.


Always jumper a 12-volt battery with another 12-volt battery. Using a larger battery could damage your car’s electronics. Never bypass a frozen battery. She could explode. If the sides of the battery bulge, it is likely frozen. Some batteries also have an indicator that shows you if the liquid inside is frozen. Car batteries give off hydrogen gas. If there’s enough gas, a stray spark could ignite it. Connect jumper cables in the correct order and the receiver battery negative cable to the engine block instead of the battery itself. Both reduce the risk of sparks and thus an explosion.