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How to Safely Jump-Start a Car

Learn how to jumpstart a car safely. Follow these four simple steps to make good, safe connections and jump a car.

how to jump a car how to jump start a carFamily Handyman
Dead or weak battery? Jump-starting a vehicle is easy and safe if you follow these four simple steps. Keep reading to learn how to jump-start a car.

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How to Jump-Start a Car

Carrying a set of jumper cables can help you help a fellow motorist—or the other way around. How to jump start a car is usually pretty simple, but it’s serious business and you have to do it right to do it safely. Every year people are seriously injured while attempting to help another driver with a “jump.” Clip this how to jump a car battery article and put it in your glove box. Then, before you even connect the cables, go through these steps for how to jump a car battery safely:

  • Make sure both batteries are the same voltage (most batteries are 12 volts) and the same polarity (both have a negative ground). You can check this information, to know how to jump a car battery, in your owner’s manual in your glove box.
  • Pull your cars close enough to each other to connect the cables, but never let the vehicles touch. This could cause a short.
  • Shut off the ignition switch, lights and accessories in both cars before you jumpstart a car. Be sure the vehicles are in park or neutral and that the parking brake is set. Wear safety glasses.
  • Don’t smoke. Sparks near a battery can cause an explosion.
  • If the weak battery is frozen, don’t try to jump it! It could explode. You can tell if it’s frozen by looking through the inspection cap to see if the water is frozen. One or more sides of the battery case will bulge if it’s frozen.
  • Make sure you can identify the positive and negative terminals of both batteries to know how to put on jumper cables. Also be sure you’ll have enough room to clamp to the cable terminals. The positive terminal is most likely connected to the car’s starting/charging system with a red cable that has a plus sign. The negative is connected to the engine of the vehicle and usually has a minus sign.

How to connect jumper cables and how to jump-start a car

how to jump start car

How to Jump a Car Photo 1: Hook-up at the weak battery

Connect to the positive cable to the positive terminal of the weak battery. Connect the negative terminal to metal on the engine for the correct way on how to attach jumper cables.

how to jump start car

How to Jump a Car Photo 2: Hook-up at the good battery

Connect to the positive cable to the positive terminal and the negative cable to the negative terminal of the good battery.

How to jump-start a car steps:

  1. Clamp the positive (red or yellow) cable to the positive terminal of the weak battery. Make sure the other end doesn’t touch any part of the car’s engine or body or you could get a dangerous spark.
  2. Clamp the other end of the positive cable to the positive terminal of the good battery.
  3. Clamp the negative cable (black) to the negative terminal of the good battery.
  4. Clamp the other end of the negative cable to a clean metal part of the engine (like a bolt head or bracket) in the car with the weak battery. Keep the clamp away from the battery, any moving parts and the fuel system.

Caution: Don’t attach the negative cable to the negative terminal of the weak battery when jumping a car battery! This common mistake could ignite hydrogen gas directly over the battery. Battery explosions can cause serious injury. Even if you’ve gotten away with it before, use a metallic engine part instead when jumping a car.

Now start the car with the good battery, let it charge the weak battery for 5 minutes, then try to start the car with the weak battery. If it doesn’t start, shut off both ignitions, make sure the cable clamps are making good contact and then try it again. When the car with the weak battery starts, wait (about 15 seconds or so) to make sure it doesn’t stall.

Disconnect the cables in the reverse order: First remove the negative cable from the car you jumped, then the negative cable from the car with the good battery. Then remove the positive cable from the car with the good battery (don’t touch a grounded part of either car with the clamp of the positive cable). Finally, remove the positive cable from the car with the weak battery. Remember, both engines will be running (with any luck!), so work carefully as you remove cables to avoid belts, fans and other moving parts.

Pro Tip: If you live in a very cold climate, buy the thickest-gauge cables you can find (the lower the number, the thicker the cable).

If it’s time to replace your car battery, check out the video below on how to replace a car battery.

Required Tools for this How to Jumpstart a Car Project

You’ll need a set of jumper cables to know how to jump a car.