When jump-starting a car with jumper cables, connect the cables in a specific order: start with the positive terminal on the dead battery, then the positive terminal on the working battery, followed by the working battery’s negative terminal, and finally a designated ground point on the disabled car. The order helps reduce the risk of sparks near a battery, which can produce flammable hydrogen gas. Because vehicle designs differ, the owner’s manual should always take priority.
Which Car Comes First When Connecting Jumper Cables?
Connect the red positive clamp to the dead car first. Then attach the other red clamp to the working car’s positive terminal. After that, connect the black negative clamp to the working car’s negative terminal. Attach the remaining black clamp to an approved, unpainted metal ground point on the disabled car—not usually to its battery’s negative terminal.
This sequence is commonly recommended for conventional 12-volt vehicles. It places the final connection away from the dead battery, where a spark is less likely to ignite battery gases. The final connection can still spark, so keep it away from the battery and follow the instructions for both vehicles.
Jumper Cable Connection Order
- Prepare both vehicles. Park them close enough for the cables to reach without stretching, but do not let the vehicles touch. Put both in Park, or in gear for a manual transmission, set the parking brakes, and switch off the ignitions and electrical accessories.
- Connect the first red clamp to the dead battery’s positive (+) terminal. The positive post is often marked with a plus sign and may have a red cover.
- Connect the second red clamp to the working battery’s positive (+) terminal.
- Connect one black clamp to the working battery’s negative (−) terminal.
- Connect the last black clamp to a manufacturer-approved ground point on the disabled vehicle. Use a solid, unpainted metal part of the engine or chassis, away from the battery, fuel system, belts, and fans. Check the owner’s manual for a designated jump-start ground point.
Keep the clamps from touching each other or moving engine parts. Follow any labels on the battery and the cable manufacturer’s instructions. If either vehicle’s manual specifies a different connection point or procedure, use that procedure instead.
Why the Connection Order Matters
A lead-acid battery can release hydrogen gas, especially while charging. Hydrogen is highly flammable. Connecting the final negative clamp to a ground point away from the battery helps move a possible spark away from the battery itself.
The sequence also helps limit accidental short circuits. If a clamp attached to the positive terminal touches metal connected to the vehicle’s body, current can take an unintended path. Careful placement, correct polarity, and keeping the clamps separated reduce that risk. Jumper cables can carry enough current to cause burns, damage electronics, or start a fire if misused.
How to Start the Disabled Car
Once all four clamps are secure, start the working vehicle if its manual allows it. Let it run for a few minutes, then try starting the disabled vehicle. Avoid prolonged cranking: if the engine does not start after a short attempt, wait briefly and try again. The vehicle manuals may set specific waiting times or limits.
If the disabled vehicle starts, leave it running and remove the cables in the reverse order of connection:
- Remove the black clamp from the disabled vehicle’s ground point.
- Remove the black clamp from the working battery’s negative terminal.
- Remove the red clamp from the working battery’s positive terminal.
- Remove the red clamp from the formerly dead battery’s positive terminal.
Keep the clamps apart while removing them, and do not let them contact moving parts. Drive or run the vehicle according to the owner’s manual, then have the battery and charging system tested if the battery was unexpectedly discharged or the problem returns. A jump-start gets the engine running; it does not repair a weak battery or a charging-system fault.
Quick Reference: Cable Order and Removal Order
| Step | Connection |
|---|---|
| 1 | Red clamp to the disabled car’s positive terminal |
| 2 | Other red clamp to the working car’s positive terminal |
| 3 | Black clamp to the working car’s negative terminal |
| 4 | Other black clamp to an approved ground point on the disabled car |
Removal: Take off the clamps in reverse order, beginning with the black clamp on the disabled vehicle’s ground point.
Where to Find the Ground Point
The correct ground point varies by vehicle. Some cars have a clearly marked jump-start post under the hood. Others specify a metal bracket, engine lifting point, or another unpainted location. The manual may show the point in a diagram, often in a section called “Jump Starting,” “Battery,” or “Emergency Starting.”
Do not assume that any metal surface is suitable. Avoid painted or plated surfaces, thin sheet metal, fuel lines, brake lines, and parts that move or become hot. If the manual does not identify a safe ground point, do not guess; use roadside assistance or a compatible jump starter according to its instructions.
Important Safety Checks Before Jump-Starting
- Check the battery condition. Do not jump-start a battery that is cracked, leaking, swollen, unusually hot, or visibly damaged. Do not proceed if it smells strongly of sulfur or rotten eggs.
- Confirm the voltage. Most passenger cars use 12-volt systems, but the manuals should confirm that the vehicles and equipment are compatible. Never connect a 12-volt vehicle to a 24-volt system.
- Check polarity and labels. Positive connects to positive for the red cable. Never reverse the clamps. Stop if terminals are unclear or corroded enough to prevent a secure connection.
- Use suitable equipment. Inspect cables for fraying, exposed wire, or damaged clamps. Follow the cable maker’s instructions and keep jewelry, loose clothing, and hands away from belts and fans.
- Protect the vehicles. Some manufacturers prohibit jump-starting another vehicle or require special procedures to protect electronic systems. Read both manuals before connecting anything.
Wear eye protection if available, and keep sparks, flames, and cigarettes away from the battery. If a battery is frozen, damaged, or leaking, do not attempt a jump-start. A frozen battery can rupture or explode when charged.
Vehicles With Remote Jump-Start Terminals
Many newer vehicles place jump-start connections under the hood even when the 12-volt battery is in the trunk, beneath a seat, or elsewhere. A remote positive post and a separate ground point may be provided to make jump-starting safer and easier. Use those specified points rather than searching for or reaching the battery directly.
Some vehicles have sensitive electronics, automatic battery-management systems, or special instructions for connecting an external power source. The owner’s manual may require the ignition to be off, prescribe a particular ground point, or warn against using another vehicle as the power source. Those directions override generic cable instructions.
Hybrid and Electric Vehicle Considerations
Many hybrids and battery-electric vehicles have a low-voltage battery, commonly 12 volts, that powers computers, locks, and control systems. A jump-start may restore that low-voltage system, but it does not charge or jump-start the high-voltage traction battery. Procedures vary widely by model, so the vehicle’s manual is essential.
Never touch, disconnect, or attach jumper cables to high-voltage components. These are commonly marked with orange cables or warning labels. Some manufacturers allow a vehicle’s 12-volt system to help another car; others prohibit it or restrict the procedure. Do not assume that a hybrid or EV can be used as the donor vehicle. Use a compatible jump pack or call roadside assistance if the manual’s directions are unclear.
Common Jump-Starting Mistakes
Connecting the Last Clamp to the Dead Battery’s Negative Post
For many conventional vehicles, the recommended final connection is a ground point on the disabled car, away from the battery. However, vehicle-specific instructions can differ. Follow the manual rather than treating this general sequence as universal.
Reversing the Red and Black Clamps
Incorrect polarity can damage vehicle electronics and batteries and may cause serious injury. Check the plus and minus markings on both vehicles before connecting. If the markings are hidden or hard to identify, stop and consult the manual.
Letting the Clamps Touch
Clamps that touch while connected can create a short circuit and intense heat. Place them so they cannot fall together, and hold the insulated handles when attaching or removing them.
Cranking for Too Long
Repeated, extended attempts can overheat the starter or cables. If the engine does not start after a few brief attempts, stop and investigate. The cause may be a failed battery, a fuel or ignition problem, or a poor cable connection—not simply a lack of charging time.
What to Do If the Car Still Will Not Start
Turn off the ignition and check that all connections are secure and correctly placed, following the manual. Do not keep trying if the cables become hot, smoke appears, the battery changes shape, or there is a strong odor. Disconnect only if it is safe to do so; otherwise, move away and call for help.
If the engine cranks slowly or not at all after a proper connection, the battery may be severely discharged or defective, the clamps may not have a good connection, or the starter or electrical system may have a fault. If the engine starts but stalls, or the battery warning light remains on, the charging system may need service. A repair shop or roadside professional can test the battery, alternator, and starting system.
When to Use a Jump Starter or Call for Help
A portable jump starter avoids connecting two vehicles, but it still requires the correct polarity and a compatible voltage. Follow its manual, including the order for attaching and removing clamps. Some units include reverse-polarity protection, but that feature is not a reason to ignore the markings.
Call roadside assistance if the battery is damaged, the vehicle’s procedure is uncertain, the vehicles are incompatible, or a jump-start does not work after careful attempts. Professional help is also appropriate when working near traffic, in poor weather, or in a location where safely positioning vehicles is difficult.
Reliable References
- National Highway Traffic Safety Administration (NHTSA) provides vehicle safety information and links to manufacturer resources.
- AAA offers roadside assistance guidance and vehicle service information.
- The vehicle owner’s manual is the primary reference for the approved jump-start terminals, grounding location, compatibility, and model-specific precautions.