To jump start a car, connect the red clamp to the dead battery’s positive terminal, the other red clamp to the good battery’s positive terminal, the black clamp to the good battery’s negative terminal, and the last black clamp to bare metal on the dead car’s engine, away from the battery. Start the running car, wait a few minutes, then start the dead car. Remove the cables in the reverse order.
What you need
- Jumper cables in good condition, ideally heavy-gauge and long enough to reach comfortably
- A running vehicle with a battery of the same voltage (12 volts on cars and light trucks), or a charged portable jump starter
- Safety glasses; batteries can vent explosive hydrogen gas
How to jump start a car, step by step
- Park the good car close without the vehicles touching, turn both off and set the parking brakes.
- Check the dead battery: do not jump a battery that is cracked, leaking, swollen or frozen.
- Connect red to the dead battery’s positive (+) terminal.
- Connect the other red to the good battery’s positive (+) terminal.
- Connect black to the good battery’s negative (-) terminal.
- Connect the last black clamp to an unpainted metal bolt or bracket on the dead car’s engine, away from the battery.
- Start the good car and let it run for two to five minutes.
- Start the dead car. If it does not start, wait a few more minutes and check the clamps, then try again.
- Remove the cables in reverse order: black from the dead car, black from the good car, red from the good car, red from the dead car.
- Drive for at least 20 to 30 minutes or put the battery on a charger.
Using a portable jump starter
Connect red to positive and black to negative or engine ground as the starter’s instructions say, switch it on and start the car. Charge the jump starter afterward so it is ready next time.
Why a car will not start even with a jump
- Single click, lights bright: often the starter or its connection; see car won’t start.
- Nothing changes: poor clamp contact, corroded terminals or a battery with a dead cell.
- Cranks but will not fire: the battery was not the problem; check fuel and spark.
If it dies again after a jump
A car that starts with a jump but goes flat again after driving usually has a charging problem rather than a bad battery; see bad alternator symptoms and battery light on. A battery that will not hold a charge overnight is usually worn out; see how long car batteries last.
Safety notes
- Never let the clamps touch each other while connected.
- Keep sparks and flames away from the batteries.
- On hybrids, electric vehicles and some newer cars, follow the owner manual; many have dedicated jump points under the hood.
- After a jump, warning lights or odd shifting can be low-voltage effects that clear once the battery is charged; see limp mode.
More guides: car won’t start, just clicks · bad starter symptoms · alternator or battery?.
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