Does the order you put jumper cables on matter?

Yes—the order matters for safety and to protect vehicle electronics. The widely accepted sequence is: connect red (positive) to the dead battery’s + terminal, red to the good battery’s +, black (negative) to the good battery’s −, and finally black to an unpainted metal ground on the dead car—away from its battery. Disconnect in the reverse order. This reduces sparks near the dead battery, lowers fire risk from hydrogen gas, and minimizes the chance of costly electrical damage.

Why the connection order matters

The sequence isn’t arbitrary. It’s designed to reduce risks that can arise in a real-world jump-start—especially on modern vehicles packed with sensitive electronics.

• Fire and explosion risk: Lead‑acid batteries can vent hydrogen gas. Making the final connection away from the dead battery keeps any inevitable spark away from that gas.
• Electronic protection: Correct order reduces voltage spikes and the chance of short circuits that can fry control modules, alternators, and sensors.
• Human safety: Proper sequencing helps prevent arcing at the terminals and accidental clamp-to-clamp contact.
• Cleaner current path: Using a chassis/engine ground on the dead vehicle often improves the quality of the connection and avoids current flowing through delicate sensors on the negative terminal.

Following the recommended order is a simple, low-cost way to avoid dangerous sparks and expensive repairs, especially on newer cars.

The correct sequence: car-to-car jump-start

Use quality, undamaged cables. Both vehicles should be in Park (or Neutral), parking brakes set, lights and accessories off, and hoods open. If your vehicle has dedicated jump posts, use those instead of the battery terminals.

1. Red to dead: Connect the red (+) clamp to the dead battery’s positive terminal (or designated positive post).
2. Red to donor: Connect the other red (+) clamp to the good battery’s positive terminal (or designated positive post).
3. Black to donor: Connect the black (−) clamp to the good battery’s negative terminal (or designated negative post).
4. Black to ground on dead car: Connect the final black (−) clamp to a solid, unpainted metal point on the dead car—such as a clean engine bracket or chassis ground point—away from the battery and fuel system. If the car provides a marked negative jump/ground post, use that.
5. Charge briefly: Start the donor vehicle and let it idle for 2–5 minutes to put some charge into the dead battery.
6. Start the dead vehicle: Try starting the dead car. If it doesn’t start, wait another few minutes and try again. Avoid cranking more than 10 seconds at a time; let the starter cool for 30–60 seconds between attempts.

Using this order keeps the final “spark” connection away from the dead battery and sets up a safer current path, especially important on modern vehicles with battery sensors.

How to disconnect (reverse order)

Once the dead vehicle is running, remove the cables in the exact reverse order to minimize sparking and protect electronics.

1. Remove the black (−) clamp from the grounded metal point on the formerly dead vehicle.
2. Remove the black (−) clamp from the donor vehicle’s negative terminal/post.
3. Remove the red (+) clamp from the donor vehicle’s positive terminal/post.
4. Remove the red (+) clamp from the formerly dead vehicle’s positive terminal/post.

Reversing the connection sequence during removal helps prevent accidental short circuits and reduces arcing near batteries.

Using a portable jump starter (jump pack)

Many modern jump packs include reverse-polarity and spark protection, but you should still follow best practices for connection order.

1. Power off the jump pack and ensure it’s adequately charged.
2. Connect red (+) clamp to the battery’s positive terminal (or positive jump post) on the dead vehicle.
3. Connect black (−) clamp to the dead vehicle’s designated ground point or a clean, unpainted engine/chassis metal surface—away from the battery.
4. Turn on the jump pack and attempt to start the vehicle. Observe any indicators or alarms on the pack.
5. After starting, power off the pack before removing clamps, then remove black (−) first, followed by red (+).

Following this approach mirrors the safety logic of car-to-car jumping while leveraging the jump pack’s protections.

Exceptions and special cases

Some vehicles require a slightly different approach. Always check the owner’s manual first for model-specific instructions.

• Dedicated jump posts: Many newer cars (BMW, Mercedes‑Benz, Ford, Toyota, etc.) provide under‑hood positive and negative jump posts even if the battery is elsewhere (e.g., trunk). Use those posts instead of the battery terminals.
• Negative battery sensor (IBS): Vehicles with an Intelligent Battery Sensor on the negative terminal should not have a clamp attached directly to that sensor. Use the marked ground point to avoid damaging the sensor or bypassing battery management.
• Hybrids and EVs: Do not attempt to jump a high‑voltage traction battery. You may jump only the 12‑volt system if the manufacturer permits it—and some hybrids/EVs should not be used as donor vehicles. Follow the manual’s specific posts and steps.
• 48‑volt mild hybrids: These vehicles still have a 12‑volt system for starting/control. Use only the designated 12‑volt jump points. Never interface with the 48‑volt circuit.
• Side‑post batteries: Ensure secure clamp connection; consider adapters if needed to avoid loose or accidental contact.
• Battery in trunk or under seat: Use the front-mounted service posts provided under the hood for safety and accessibility.
• Frozen, cracked, or leaking battery: Do not jump-start. Replace the battery and clean/repair as needed; jumping a compromised battery is dangerous.

While the principles are consistent, adhering to the vehicle’s designated posts and any battery-management requirements is essential for safe, successful starts.

Safety checks and troubleshooting

Safety checklist before you connect

Run through these quick checks to avoid common hazards and protect both vehicles.

• Inspect batteries for bulging, cracks, or leaks; abort if present.
• Remove loose jewelry and keep clothing, hair, and cables clear of belts/fans.
• Confirm polarity: identify + and − clearly before clamping.
• Ensure clamps never touch each other when connected to a battery.
• Keep sparks, smoking, and open flames away from the battery area.
• If the dead battery is more than 5–7 years old or repeatedly discharges, consider replacement—jumping may be a temporary fix.
• After starting, let the engine run 20–30 minutes or drive to recharge; a brief idle may not fully recover the battery.

These precautions significantly reduce the likelihood of injury or electrical damage while improving your chances of a successful jump-start.

If you connect out of order or reverse polarity

Mistakes happen. If you realize the cables are reversed or you deviated from the sequence, act immediately and cautiously.

1. Do not start either vehicle. If running, turn them off at once.
2. Carefully remove the cables in the safest sequence available—break the connection at the ground/negative side first to stop current flow.
3. Inspect main fuses and fusible links; reverse polarity can blow them instantly.
4. Check for warning lights or electrical issues on both vehicles; if present, have the systems scanned.
5. Before attempting again, recheck polarity and follow the correct order precisely.

Quickly removing the incorrect connections and assessing for damage can prevent a minor mistake from becoming a major repair.

Summary

The order absolutely matters: connect red to dead +, red to donor +, black to donor −, and black to a ground on the dead car—then remove in reverse. This method reduces sparks near the battery, protects electronics, and improves safety. When in doubt, use the vehicle’s designated jump posts and follow the owner’s manual, especially for vehicles with battery sensors, hybrids, EVs, and 48‑volt systems.

Should the car be on before connecting jumper cables?

Park both cars facing each other, close but not touching, before connecting cables. Turn off both engines and engage the parking brakes. Safety first!

Do I connect black or red first?

When connecting jumper cables to a car with a dead battery, always connect the red/positive cable first to the positive (+) terminal of the dead battery, and then to the positive terminal of the working battery. The negative (black) cables should be connected last, with one to the negative terminal of the working battery and the other to an unpainted metal surface on the dead car’s engine block or frame to complete the circuit.
 
This video demonstrates how to safely connect jumper cables to a car battery: 51sStan CravensYouTube · Oct 9, 2018
Step-by-Step Guide to Connecting Jumper Cables:

1. Turn off both vehicles: Opens in new tabEnsure the ignition keys are in the off position in both the car with the dead battery and the donor car. 
2. Connect the red (positive) cable to the dead battery: Opens in new tabAttach one red clamp to the positive (+) terminal of the dead battery. 
3. Connect the red (positive) cable to the donor battery: Opens in new tabAttach the other red clamp to the positive (+) terminal of the good battery on the donor vehicle. 
4. Connect the black (negative) cable to the donor battery: Opens in new tabAttach one black clamp to the negative (-) terminal of the donor vehicle’s good battery. 
5. Connect the black (negative) cable to the dead car’s frame: Opens in new tabAttach the final black clamp to an unpainted, unmoving metal part of the engine block or frame of the car with the dead battery. A slight spark may occur, which is normal. 

Why this order?

• Red first: Connecting the positive (red) cable to both batteries first creates a complete circuit without completing the negative side. 
• Last connection to metal: The last black clamp is attached to an unpainted metal surface on the dead car’s frame, not the negative terminal. This minimizes the risk of sparks, as the battery releases hydrogen gas that could cause an explosion. 

In what order should I connect battery cables?

“Positive first, then negative. When disconnecting the cables from the old battery, disconnect the negative first, then the positive.

What happens if you put jumper cables on in the wrong order?

Connecting jumper cables in the wrong order, which usually means reversing the polarity (positive to negative), can cause a short circuit, blown fuses, burnt wiring, and even damage to expensive electronics like the powertrain control module or alternator in both vehicles. In the worst-case scenarios, it can lead to a fire or the battery exploding due to the rapid flow of high current.
 
This video demonstrates what happens when jumper cables are connected incorrectly: 1mWorld MechanicsYouTube · Feb 19, 2016
Common Consequences of Incorrect Connection

• Electrical Damage: Opens in new tabThe most frequent damage involves blown fuses and fried electronic components, such as the car’s computer (ECU), transmission control unit, or alternator rectifiers. 
• Wiring and Cable Damage: Opens in new tabHigh currents can overheat and melt the jumper cables themselves or the vehicle’s internal wiring. 
• Component Damage: Opens in new tabExpensive parts like the starter solenoid or other sensitive electronics can be permanently destroyed by the reverse polarity. 
• Sparks and Fire Risk: Opens in new tabA short circuit creates a very high current, which generates significant heat and can cause sparks that may ignite flammable gases around the battery, leading to a fire. 
• Battery Explosion: Opens in new tabBatteries can release hydrogen gas, and a reverse polarity connection creating a spark could trigger an explosion. 

Preventing Damage

• Follow the Correct Procedure: Always connect the cables in the correct order: red to positive (+) terminals first, then black to negative (-) terminals or a grounded point away from the battery. 
• Connect the Final Cable to a Ground: As a safety measure, connect the final black negative clamp to a piece of unpainted metal on the engine block or chassis of the dead car, rather than directly to the negative battery terminal. 
• Be Aware of the Risks: Understand that even a momentary reverse polarity can cause serious issues in modern vehicles with complex electronics.