How To Safely Jump Start a Car With Jumper Cables

Follow these simple steps to make good, safe connections and jump a car.

How to Jump Start a Car

Carrying a set of jumper cables and knowing how to use them lets you help out a fellow motorist in need — or the other way around.

Jump starting a car is usually simple, but it’s serious business — you have to do it right to do it safely. Every year people are seriously injured attempting to “jump” another vehicle. Before you connect the cables, go through this safety checklist:

  • Make sure both batteries are the same voltage (most are 12 volts) and the same polarity (both have a negative ground). You can check this information in your owner’s manual.
  • Pull your cars close enough to connect the cables, but never let the vehicles touch. This could cause a short.
  • Shut off the ignition switch, lights and any accessories in both cars before attempting a jump start. Be sure both vehicles are in park or neutral and the parking brakes are 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 peering 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. Also be sure you have enough room to clamp your cables to the battery terminals. The positive terminal, most likely connected to the car’s starting/charging system, has a red cable with a plus sign. The negative terminal, connected to the engine, and usually has a minus sign.

How To Jump Start a Car:

  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 engine or body of the vehicle 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, moving parts and the fuel system.
    1. 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, attach to a metallic engine part instead.
  5. Now start the car with the good battery. Let it charge the weak battery for five minutes, then try to start the car with the weak battery. If it doesn’t start, shut off both engines, make sure the cable clamps are making good contact and then try it again.
  6. When the car with the weak battery starts, wait about 15 seconds or so before disconnecting the cables to make sure it doesn’t stall. Here’s a safe way to use jumper cables.

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.

Harrison Kral
After spending his college summers pouring concrete and building decks, Harrison Kral decided to find a way to put his insider knowledge of construction to use…. just in an air-conditioned setting. He’s an established writer and editor in the DIY space who has written extensively on the home building industry, the housing market, and general DIY trends.