Connect the red cable to the dead battery's positive terminal first, then to the good battery's positive terminal. Then connect the black cable to the good battery's negative terminal, and finally to an unpainted metal surface on the dead car's engine. This order matters because it prevents sparks near the battery.
A dead car battery is one of the few things you can fix roadside in minutes without calling a tow truck. Booster cables are two insulated wires with clamps on each end — one red (positive) and one black (negative). The order you connect them prevents electrical arcs that could ignite battery gases or damage your car's electronics.
You will need a second car with a working battery, booster cables in good condition (no cracked insulation or corroded clamps), and about five minutes. Both cars should be off before you start connecting anything.
Key Takeaways
- Always connect red to the dead battery's positive terminal first, then to the working battery's positive terminal.
- Connect black to the working battery's negative terminal, then to bare metal on the dead car's engine — never to the negative terminal itself.
- Start the working car and let it run for two to three minutes before starting the dead car.
- Remove cables in reverse order: black from the dead car first, then black from the working car, then red from both.
- Drive for at least twenty minutes after a jump to let the alternator recharge the battery.
Position both cars and locate the battery terminals
Park the working car close enough that the cables will reach both batteries — usually three to four feet apart. Open both hoods and locate the battery in each car. Car batteries have two terminals on top: one marked with a plus sign (+) or red plastic cover (positive), and one marked with a minus sign (−) or black plastic cover (negative).
If the terminals are corroded white or blue-green, scrape them lightly with a wrench or the edge of a coin to expose clean metal. Corrosion blocks electrical contact and makes the jump less effective. If the positive terminal has a plastic cover, remove it by hand or pry it off gently.
Connect the red cable to both positive terminals
Take the red cable and clamp one end firmly onto the positive terminal of the dead battery. You should hear or feel a click, and the clamp should not move when you tug it. The positive terminal is usually larger than the negative one and marked with a plus sign or red color.
Walk to the working car and clamp the other end of the red cable to its positive terminal with the same firm grip. Do not let the two red clamps touch each other or any metal part of either car — this creates a short circuit. If you drop the cable, pick it up and start over; do not try to reposition it while it is touching metal.
Connect the black cable to the working battery and engine ground
Take the black cable and clamp one end to the negative terminal of the working battery. This is the safe starting point because the working battery is not under stress. Again, make sure the clamp is tight and does not move.
Now clamp the other end of the black cable to an unpainted metal surface on the dead car's engine — a bolt, bracket, or the engine block itself. Do not clamp it to the negative terminal of the dead battery. This step is critical: connecting to bare engine metal instead of the battery terminal prevents sparks directly above the battery, where hydrogen gas can collect and ignite. Choose a spot at least twelve inches away from the battery if possible.
Start the working car and wait before starting the dead car
Start the working car and let it run for two to three minutes. This gives the alternator time to build up charge in its battery and stabilize the electrical system. You should see the engine running smoothly and hear normal idle sounds.
After two to three minutes, try to start the dead car. Turn the key or press the start button as you normally would. If the engine does not turn over after five to ten seconds of cranking, stop and wait another minute before trying again. Repeated cranking drains both batteries and can overheat the starter motor.
Remove the cables in the correct order
Once the dead car's engine is running, let both cars idle for another minute. Then remove the cables in this exact order: black clamp from the dead car's engine, black clamp from the working car's negative terminal, red clamp from the working car's positive terminal, and finally red clamp from the dead car's positive terminal.
Remove each clamp by twisting it slightly side to side and pulling straight away from the terminal. Do not yank or pull at an angle, which can bend the terminal or damage the battery case. Coil the cables loosely and store them in the working car.
Drive to recharge the battery
Drive the previously dead car for at least twenty to thirty minutes without stopping. The alternator charges the battery while the engine runs, and a longer drive gives it more time to recover. If the car dies again within a few hours, the battery is likely too weak to hold a charge and will need replacement.
If the car starts and runs normally, the jump worked and the battery may still be good. However, a battery that dies suddenly for no reason often fails again soon. Consider having it tested at an auto parts store or mechanic within a few days to know whether replacement is coming.
Frequently Asked Questions
What if the cables spark when I connect them?
A small spark when the final connection is made is normal. A large spark or continuous sparking means you connected something in the wrong order or to the wrong terminal. Stop when ready, remove all cables, and start over from the beginning. Check that you used red for positive and black for negative.
Can I connect the black cable to the negative terminal of the dead battery instead of the engine?
You can, but it is riskier. Hydrogen gas collects above the battery during discharge, and a spark near the negative terminal can ignite it. Connecting to bare engine metal moves the spark source away from the gas. If you must use the negative terminal, make sure the battery case is not cracked and the terminal is clean.
How long should I wait after jumping before driving?
You can drive when ready after the engine starts, but let both cars idle for at least one minute first. Then drive for twenty to thirty minutes without stopping to give the alternator time to recharge the battery fully. Short trips do not give the battery enough charging time.
What if the car still will not start after I connect the cables?
Check that both clamps are tight and making full contact with clean metal. If they are, wait another two to three minutes and try again. If the engine still does not crank, the battery may be too dead to jump, or the problem may not be the battery — it could be a bad starter or dead alternator. You will likely need a tow truck.
Do I need to disconnect the negative terminal of my car before jumping it?
No. Modern cars have computers and electronics that can be damaged if you disconnect the negative terminal while the engine is running. Just connect the booster cables as described and let the working car's battery do the work. Disconnecting is an older practice that is no longer necessary or recommended.