How to Hook up Jumper Cables

Co-authored by Duston Maynes

Your battery can be too weak to start your car for a number of reasons, including a loss of charge from cold weather, age, or leaving the lights on overnight. Whatever the cause, you can use jumper cables to connect the dead battery to a live one. Make sure both batteries are the same size, then carefully begin clamping the cables in place. The dead battery may then receive enough of a charge to get the car started again.

Part 1

Part 1 of 3:

Exposing the Batteries

1
Park the vehicles so the batteries are near each other. Drive the vehicle with the live battery, which is the donor car, towards the vehicle with the dead battery. The battery is typically located underneath the car’s hood, so you can either park the cars next to each other or facing one another. Don’t let the cars touch, though!^{[1]
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Check the owner’s manual if you are unable to locate the battery. It should tell you where the battery is and how to access it.
2
Engage the parking brake on both cars. The parking brake ensures that the cars stay in place as you jump the battery. Use the gear stick if your car has one. Shift the car to “P” or “Park” to engage the brake. Setting the car to “N,” or “Neutral,” will also prevent it from rolling. If your car has manual transmission, set it to neutral, then engage the emergency brake.^{[2]
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- The emergency brake may be located near the gear stick or gas pedal.
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3
Turn the cars off and remove the keys. Make sure the donor car is completely off. You should hear the engine shut down and can test the radio to see that it doesn’t have any power running to it. Also take the key out of the car with the dead battery so it can’t start up when the jumper cables are attached.^{[3]
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- Doing this protects both engines from power surges and reduces the risk of electrical shock.
4
Check the batteries to make sure they are the same voltage. The voltage will be printed in a visible location, usually on a white or yellow sticker on top of the battery. It will say something like “12V.” The live battery needs to match the dead battery or else it can send a dangerous current that burns out the car’s systems.^{[4]
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- Batteries with similar voltages will be the same size. Still, look for the voltage on the label to avoid possible damage.
- If you aren’t sure about using a battery, avoid the risk if possible. Try to find a different donor battery or use a rechargeable battery pack.
5
Locate the positive and negative battery terminals in each car. The cables leading to the positive terminal are almost always red. The negative terminal’s cables are black. If you’re not sure, the battery will have a “+” and “-” sign on it to mark the positive and negative terminals, respectively. The red cables lead to the “+” terminal and the black cables go to the “-” terminal.^{[5]
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- Check the terminals for corrosion first. It looks like white, green, and blue powder. Clean the terminals by wiping them with a rag or wire brush.

Part 2

Part 2 of 3:

Connecting the Cables

1
Separate the jumper cable clamps by laying them on the ground. Position the cables flat on the ground, stretching them out between the 2 cars. Move the clamps so they aren’t touching each other. Any accidental contact can cause your car’s electrical system to short circuit.^{[6]
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- Leads on jumper cables are often made in different lengths to prevent them from touching. If they are the same length, make sure they have not been modified or damaged in any way.
2
Clamp a red clamp to the positive terminal of the dead battery. Leave the rest of the jumper cable on the ground as you bring the clamp over to the car. Double-check the “+” and “-” labels on the battery before attaching the clamp. Squeeze the clamp to open it, then fit it securely around the metal terminal.^{[7]
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Expert Source

Duston Maynes
Automotive Repair Specialist
Expert Interview. 14 July 2021.}
- On some vehicles, you may have to remove a plastic cover from the positive battery terminal before you can make this connection. You remove it by twisting it counterclockwise by hand.
- Connect each clamp 1 at a time. Go slowly in order to avoid mistakes that can damage the vehicles.
3
Secure the other red clamp to the positive terminal on the donor battery. Carry the clamp to the other car so you can fit in on the correct terminal. Make sure it is secure so it won’t slip off when the engine is activated later.^{[8]
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- Remember to match red to red and positive terminal to positive terminal when applying the red clamps.^{[9]
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  Expert Source
  
  Duston Maynes
  Automotive Repair Specialist
  Expert Interview. 14 July 2021.}
4
Connect a black clamp to the negative terminal on the donor battery. Retrieve the black clamp and bring it back to the live battery. The black clamp fits directly on the “-” terminal on the battery. As long as it doesn’t touch the “+” terminal or red clamp, you will be fine.^{[10]
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Expert Source

Duston Maynes
Automotive Repair Specialist
Expert Interview. 14 July 2021.}
- If you attach a clamp incorrectly, stop before you start the cars. Remove the clamps carefully, working 1 at a time to avoid touching them together.
5
Clamp the other black lead to an unpainted metal surface in the car. The black clamp does not connect to a battery terminal. Instead, find a spot such as a clean bolt in the engine block. You may also place the clamp on an unpainted part of the car’s body underneath the hood.^{[11]
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Expert Source

Duston Maynes
Automotive Repair Specialist
Expert Interview. 14 July 2021.}
- Avoid connecting this clamp to the dead battery unless you have no other choice. This produces a spark that can ignite hydrogen fumes after the car is turned on.
- Don’t dig too far down to find a metal surface. The fuel lines are down there and you are better off keeping the clamp away from them.
- Make sure the jumper cable doesn’t hang down into the engine compartment, since it can get caught by the moving parts there.

Part 3

Part 3 of 3:

Starting the Cars

1
Start the donor vehicle and let it idle for a few minutes. Use the ignition key to start the engine. The electrical systems, such as the lights and radio, will start while electricity flows to the dead battery. Give the battery at least 30 seconds to build power before you attempt to start the other car.^{[12]
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- Depending on the dead battery’s age and condition, it may require more time to charge.
- Step on the gas pedal to run the RPM up to about 3,000 if you want to drive more power towards the dead battery.
2
Turn on the dead car’s engine. Turn the key in the ignition to activate the car. Right away, the electrical systems should activate. If the lights, radio, or other electrical components don’t come on, you may need to give the battery more time. Shut off the car, make sure the cables are attached properly, and then try revving the working car to increase the power supply.^{[13]
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- If the car doesn’t start after repeated attempts, your car may have a different problem. It could have a blown fuse.
- If the car’s lights come on but the engine won’t start, the battery is fine. You may hear the engine make a clicking noise as you try to start it. This could be because of a faulty starter.
3
Disconnect the jumper cables in reverse, starting with the black clamps. Remove the cables in the exact opposite order from earlier. Start with the negative grounding cable you attached to a metal component. Remove the black clamp, followed by the red clamp, on the donor battery. Finish by removing the red clamp on the newly-charged battery.^{[14]
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- Leave the car running so it has time to continue charging or else you will need to jump it again.
- Be careful when handling the cables. Make sure the clamps do not touch until all of them are removed from the batteries.

Expert Q&A

Question

Why don't you connect the negative when jumping a car?

Duston Maynes
Automotive Repair Specialist
Duston Maynes is an Automotive Repair Specialist at RepairSmith. Duston specializes in leading a team that handles a variety of automotive repairs including replacing spark plugs, front and rear brake pads, fuel pumps, car batteries, alternators, timing belts, and starter motors. Duston holds an Associate’s degree in Automotive/Diesel Technology from The Universal Technical Institute of Arizona and is a Certified Diagnostic Technician and Automobile Mechanics Technician through BMW STEP. RepairSmith received The 2020 Big Innovation Award by Business Intelligence Group and The Startup of the Year by the American Business Awards. RepairSmith was also included in Built in LA’s 50 Startups to Watch and The Business Intelligence Group’s 52 Names Leading the Way in Customer Service. RepairSmith offers in-home services to provide car owners convenient and complete auto repair everywhere.

Duston Maynes

Automotive Repair Specialist

Expert Answer

Grounding the negative on the dead battery allows it to charge without completing the circuit, which can be dangerous for your car's system. If you complete the loop, the electricity can spike your system and damage your alternator.

Warnings

Avoid jump-starting a frozen battery. It may explode. If you can open the battery, look to see if the liquid inside of it has frozen. Also, if the battery's sides bulge, it is likely frozen.

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Car batteries discharge explosive hydrogen gas, so avoid smoking near them. Also make sure the black grounding cable is not attached to the negative terminal on the dead battery.

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