Attach the red cable to the positive terminal first, then the black cable to the negative terminal
Jump cables connect two car batteries in a specific order to safely transfer power from a working battery to a dead one. The positive terminal (marked with a + sign and usually red) gets the red cable first. The negative terminal (marked with a − sign and usually black) gets the black cable second. This order matters because reversing it can damage both cars' electrical systems or cause sparks near the battery.
The working car's battery supplies power through the cables to restart your dead battery. Both terminals are metal posts that stick up from the top of the battery case. On most cars, the battery sits in the engine bay on the driver's or passenger's side. You will need to open the hood and locate both batteries before you begin.
Key Takeaways
- Always connect the red cable to the positive terminal of the dead battery first, then to the positive terminal of the working battery.
- Connect the black cable to the negative terminal of the working battery second, then to an unpainted metal surface on the dead car's engine (not the negative terminal itself).
- Remove cables in reverse order: black cable off the dead car first, then black off the working car, then red off the working car, then red off the dead car.
- If either battery terminal is corroded or covered in white or blue-green buildup, clean it with a wire brush or baking soda solution before connecting cables.
The correct order for connecting jump cables
Follow these steps in order. Skipping steps or changing the sequence can create electrical damage or fire risk.
- Red cable to dead battery's positive terminal: Clamp the red cable's positive clamp (marked + or red) onto the positive terminal of the dead battery. Push down firmly until the clamp grips the metal post. You should hear or feel a click.
- Red cable to working battery's positive terminal: Clamp the other end of the red cable onto the positive terminal of the working battery. Again, push down firmly.
- Black cable to working battery's negative terminal: Clamp the black cable's negative clamp (marked − or black) onto the negative terminal of the working battery. This is the second battery, not the first.
- Black cable to unpainted metal on dead car's engine: Instead of clamping to the dead battery's negative terminal, clamp the other end of the black cable to an unpainted metal bolt, bracket, or surface on the engine block or frame of the dead car. This grounds the circuit safely and reduces spark risk near the battery. Look for a bolt head or metal surface at least 12 inches away from the battery.
Once all four clamps are find, start the working car and let it run for 2 to 3 minutes. Then start the dead car. If it does not start after 30 seconds, wait another minute and try again. Do not crank the starter for more than 10 seconds at a time.
Removing cables in the correct reverse order
Disconnecting in the wrong order can send a power surge through the working car's electrical system. Remove cables in this exact sequence:
- Black cable clamp off the dead car's engine
- Black cable clamp off the working car's negative terminal
- Red cable clamp off the working car's positive terminal
- Red cable clamp off the dead car's positive terminal
After you remove the cables, keep the previously dead car running for at least 20 minutes. This gives the alternator time to recharge the battery. If the car dies again within a few hours, the battery may need replacement or the alternator may not be charging properly.
Identifying battery terminals when they are corroded or hard to see
Battery terminals can become covered in white, blue-green, or gray crusty buildup called corrosion. This buildup prevents a good electrical connection and can stop the jump from working. If you see corrosion, clean it before connecting cables.
Mix one tablespoon of baking soda with one cup of water. Dip an old toothbrush or wire brush into the mixture and scrub the terminal posts and the inside of the cable clamps. Rinse with clean water and dry with a cloth. If corrosion is heavy, you may need a wire brush alone or a terminal cleaning tool from an auto parts store.
If you cannot see the terminals clearly because they are recessed under a plastic cover, remove the cover by hand or with a wrench. Most battery covers pull straight up or unscrew. Once the terminals are visible, you can attach the cables.
What to do if the jump does not work
If the dead car does not start after 3 to 5 minutes of trying, stop and wait 10 minutes before trying again. Repeated cranking drains the working battery and generates heat that can damage both batteries.
Check that all four cable clamps are tight and making full contact with their terminals. Wiggle each clamp slightly — if it moves easily, it is not clamped down hard enough. Tighten it and try starting again.
If the car still will not start, the battery may be too dead to jump, the alternator in the working car may not be strong enough, or the dead car may have a different problem (bad starter, fuel pump failure, or ignition switch issue). In this case, call a towing service or roadside information. Continuing to jump may overheat the batteries or damage the working car's electrical system.
Safety steps before you connect cables
Turn off both cars completely before you touch the cables. Remove any metal jewelry, watches, or rings — if they touch both a terminal and a metal part of the car at the same time, they can conduct electricity and cause a burn.
Make sure both batteries are in good condition. If either battery case is cracked, leaking, or swollen, do not attempt a jump. A damaged battery can explode or leak acid. Call for a tow instead.
Keep the cables away from moving engine parts like belts and fans. Do not let the two cable clamps touch each other while they are connected to the batteries — this creates a short circuit and can spark or damage both cars.
Frequently Asked Questions
Can I connect the black cable to the negative terminal of the dead battery instead of the engine?
You can, but it is riskier. Connecting to the negative terminal itself can create a spark near the battery, which is dangerous if the battery is leaking hydrogen gas. Connecting to an unpainted metal surface on the engine block is safer because it grounds the circuit away from the battery. If you must use the negative terminal, make sure the battery case is not cracked or leaking.
What if I cannot find an unpainted metal surface on the dead car's engine?
Look for a bolt head, bracket, or strut tower that is bare metal (not painted). Avoid plastic, rubber, or painted surfaces. If the entire engine bay is painted, you can use the negative terminal of the dead battery as a last resort, but ground yourself first by touching the car's frame to discharge any static electricity.
Do I need to remove the battery terminals before jumping?
No. The cables clamp onto the terminals from the outside. You do not need to remove or disconnect anything. Just open the hood, locate the terminals, and clamp the cables on.
How long should I wait after jumping before I drive?
Drive when ready after the car starts, but keep driving for at least 20 to 30 minutes so the alternator can recharge the battery. Stopping right away gives the battery no time to recover, and it may die again when you try to start the car later.
Can jump cables damage my car's computer or electronics?
If you connect them in the correct order and remove them in the correct reverse order, the risk is very low. Reversing the order or letting the clamps touch each other can send a power surge that damages computers, radios, or other electronics. This is why the order matters.