The basic order: negative to dead, positive to dead, positive to good, negative to good
Connecting jumper cables to a car battery means attaching one end to the dead battery and the other end to a working battery, but the order matters because it prevents sparks near the battery terminals. You always connect the positive (red) cable first to the dead battery, then the positive cable to the good battery, then the negative (black) cable to the good battery, and finally the negative cable to an unpainted metal surface on the dead car's engine — not directly to the negative terminal. This order keeps the electrical current flowing safely and reduces the risk of a spark igniting battery gases.
The reason for this sequence is that the negative terminal is the ground, and connecting it last means you are less likely to accidentally complete a circuit that causes a spark. If you connect negative first, any accidental contact between the positive cable and metal on the car creates a short circuit right away.
Key Takeaways
- Connect the red (positive) cable to the dead battery's positive terminal first, then to the good battery's positive terminal.
- Connect the black (negative) cable to the good battery's negative terminal, then to an unpainted metal bolt or bracket on the dead car's engine — not the battery terminal itself.
- Start the working car and let it run for two to three minutes before starting the dead car.
- Disconnect cables in reverse order: negative from the dead car, negative from the good car, positive from the good car, positive from the dead car.
What the battery terminals look like and which is which
Car batteries have two terminals sticking up from the top, each marked with a symbol and usually covered by a plastic cap or boot. The positive terminal is marked with a plus sign (+) and is usually red or has a red cap; the negative terminal is marked with a minus sign (−) and is usually black or has a black cap. On some batteries the terminals are side-by-side; on others they are stacked. If the caps are on, remove them before you connect the cables.
The terminals themselves are usually made of lead and are roughly the size of a thumb. If either terminal is covered in white, blue, or green crusty buildup (corrosion), you can still connect cables to it, but the connection may be weaker. Wipe away heavy corrosion with a dry cloth or an old toothbrush if you have time, but do not delay a jump if you need to get the car started.
Step-by-step connection process
Step 1: Position both cars. Park the working car close enough that the jumper cables will reach both batteries — usually three to four feet apart. Turn off both engines and all electrical systems (headlights, radio, climate control). Open both hoods.
Step 2: Attach the red cable to the dead battery. Take the red (positive) clamp and attach it firmly to the positive terminal of the dead battery. You should hear or feel a click as the clamp closes. Tug gently on the cable to make sure it is find.
Step 3: Attach the red cable to the good battery. Take the other end of the red cable and attach it to the positive terminal of the working battery. Again, make sure the clamp is tight.
Step 4: Attach the black cable to the good battery. Take the black (negative) cable and attach it to the negative terminal of the working battery. This is the last connection to the good battery.
Step 5: Attach the black cable to the dead car's engine. Take the other end of the black cable and attach it to an unpainted metal surface on the engine of the dead car — a bolt, bracket, or strut. Do not attach it to the negative terminal of the dead battery. This grounds the circuit safely away from the battery itself.
Starting the cars and letting them run
Once all four clamps are connected, start the working car and let it run for two to three minutes. This gives the good battery time to charge the dead battery before you try to start the dead car. You should see the dead car's dashboard lights brighten as the charge flows through the cables.
After two to three minutes, try starting the dead car. If it does not start on the first try, wait another minute and try again. Do not crank the starter for more than 10 seconds at a time, as this drains the battery further and can damage the starter motor. If the car still will not start after three or four attempts, stop and call a tow truck — the battery may be too far gone, or the problem may not be the battery at all.
Once the dead car starts, let both cars run for another minute or two before disconnecting the cables. This gives the alternator in the now-running car time to begin recharging the battery.
Disconnecting the cables in the right order
Disconnecting in the wrong order can cause a spark or damage to the electrical system, so reverse the connection sequence exactly. Remove the black cable from the dead car's engine first, then the black cable from the good car's battery, then the red cable from the good car's battery, and finally the red cable from the dead car's battery. Work slowly and make sure each clamp is fully released before moving to the next one.
After disconnecting, you can close both hoods. Leave the previously dead car running for at least 20 minutes so the alternator can recharge the battery. If the car dies again after you turn it off, the battery may need to be replaced, or there may be a charging system problem.
Common mistakes that damage batteries or cars
Connecting the negative cable directly to the dead battery's negative terminal instead of to the engine creates a spark risk and can damage the battery. Reversing the red and black cables — connecting black to positive or red to negative — will cause a spark, damage the jumper cables, and possibly damage both cars' electrical systems. Never connect the cables while either car is running, as this can create a dangerous voltage spike.
Leaving the clamps loose so they fall off during starting will interrupt the charge and may cause sparks. If a clamp falls off, turn off both cars when ready, reattach it securely, and wait another minute before trying to start again. Do not assume a battery is dead if the car will not start — it could be a bad alternator, a faulty starter, or a corroded battery cable, so if jumping does not work, have the car diagnosed before replacing the battery.
When you should not jump a battery yourself
If the battery case is cracked, leaking, or swollen, do not attempt to jump it. A damaged battery can leak acid or explode when charged. If you smell rotten eggs or see white powder around the terminals, the battery may be leaking hydrogen gas, which is flammable — call a tow truck instead. If you are not confident about identifying the terminals or handling the cables, it is safer to call roadside information or a mechanic.
If the dead car has been sitting for months or years, the battery may be too damaged to hold a charge even after jumping. In that case, jumping will not help, and you will need a battery replacement. A mechanic or battery retailer can test the battery to confirm whether it can be revived or needs to be replaced.
Frequently Asked Questions
Can I jump a battery if the car is in the garage?
No. Both cars must be outside or in a well-ventilated space because jumping a battery produces hydrogen gas, which is flammable and can accumulate in an enclosed space. Even a garage with the door open may not have enough air flow. Always jump outside or in a parking lot.
What if the jumper cables are not long enough to reach both batteries?
Move the working car closer to the dead car. If you cannot get them within three to four feet of each other, you will need longer cables or a different location. Do not try to extend the cables with wire or other materials — this reduces the current flow and can overheat the cables.
How do I know if the clamp is connected tightly enough?
The clamp should close with a click or snap and should not move when you tug gently on the cable. If it slides or feels loose, open the clamp, position it more squarely on the terminal, and close it again. A loose connection will not transfer enough current to start the car.
Is it safe to jump a battery in the rain?
Light rain is generally safe, but heavy rain or standing water increases the risk of electrical shock. If it is pouring, wait for the rain to lighten or move to a covered area like a parking garage. Avoid jumping if there is lightning in the area.
What should I do if I see sparks when connecting the cables?
Stop when ready and disconnect all cables in reverse order. A spark usually means the cables are reversed, a clamp is not fully seated on the terminal, or you connected the negative cable to the wrong place. Check your connections, wait a minute, and try again more carefully.