How to Use Jump Leads Safely and Correctly

The correct way to use jump leads is to connect the red lead to the positive (+) terminal of the flat battery, then the red lead to the positive (+) terminal of the donor battery, connect the black lead to the negative (−) terminal of the donor battery, and finally connect the other black lead to a clean, unpainted metal ground on the dead car away from the battery; start the donor car, wait a few minutes, then start the dead car and remove the leads in the reverse order. This step-by-step approach, recommended by major motoring organizations, minimizes sparks and protects sensitive electronics in modern vehicles.

What You Need

Before attempting a jump start, make sure you have the right equipment and that both vehicles are suitable for a 12-volt jump. The following items and conditions help ensure a safe, effective boost.

• A set of heavy-duty, well-insulated jump leads (4–6 gauge/25–40 mm², with clean, tight clamps)
• A donor vehicle with a healthy 12V battery of similar voltage and capacity (or a quality jump pack)
• Eye protection and gloves
• Owner’s manuals for both vehicles (to locate correct terminals and any designated grounding points)
• A safe, ventilated area away from traffic, flames, or smoking

Having the proper gear and a compatible donor source reduces the risk of damage or injury and improves the odds of a successful start.

Step-by-Step: The Connection Order That Protects You and the Car

Before You Connect

Quick checks beforehand can prevent dangerous mistakes and protect electronics such as ECUs, alternators, and battery sensors common in modern cars.

• Confirm both systems are 12V; do not jump a 6V or 24V system with a 12V source.
• Inspect the flat battery: do not jump if it’s cracked, leaking, swollen, or frozen—call roadside assistance.
• Turn off all electrics (lights, infotainment, climate) in both vehicles; set parking brakes; place transmissions in Park (auto) or Neutral (manual).
• Keep cables clear of fans, belts, and other moving parts; remove metallic jewelry from hands/wrists.
• Locate designated jump points if provided; many newer cars have under‑bonnet posts and a specific ground stud.

If anything looks unsafe or unclear, stop and consult the vehicle manuals or a professional service.

Connecting the Leads (Correct Sequence)

Follow this order to minimize sparks near the battery and avoid reversed polarity, which can instantly damage electronics.

1. Red clamp to the positive (+) terminal of the flat battery (or its positive jump post).
2. Red clamp to the positive (+) terminal of the donor battery (or donor positive post).
3. Black clamp to the negative (−) terminal of the donor battery (or donor negative post).
4. Black clamp to a solid, clean, unpainted metal point on the engine block or chassis of the car with the flat battery—away from the battery and fuel system. Use the manufacturer’s recommended ground point if provided.

This sequence reduces the chance of igniting hydrogen gas that can be present around batteries and preserves battery monitoring systems on modern cars.

Starting and Removing (Reverse Sequence)

Allow some charge to flow before cranking the dead engine, then remove the leads in the reverse order to prevent arcing.

1. Start the donor vehicle and let it idle for 3–5 minutes; lightly raise revs to 1,500–2,000 rpm if safe to do so.
2. Attempt to start the vehicle with the flat battery. If it doesn’t start, wait another 2–3 minutes and try again.
3. Once started, keep both vehicles idling for a minute to stabilize voltage.
4. Remove the leads in reverse order: first the black clamp from the grounded point on the previously flat vehicle, then the black clamp from the donor negative, then the red clamp from the donor positive, and finally the red clamp from the previously flat battery.
5. Keep the revived engine running for at least 20–30 minutes (preferably by driving) to replenish the battery.

Reversing the removal order limits the risk of accidental short circuits and ensures a smooth handover from the donor supply to the revived alternator.

Important Safety Rules and Common Mistakes

These are the pitfalls that most often lead to damage or injury, along with best practices that motoring clubs and manufacturers emphasize.

• Never let clamps touch each other or metal bodywork while attached.
• Do not connect the final (black) clamp to the flat battery’s negative terminal—use a clean chassis/engine ground instead.
• Avoid jumping if batteries differ in system voltage or if the dead battery shows physical damage or is frozen.
• Check polarity carefully: red to +, black to −. Reversed polarity can fry ECUs, sensors, and alternators.
• Use designated jump posts in cars with battery monitoring (IBS) or in vehicles where the 12V battery is difficult to access.
• Switch off high-draw accessories; don’t crank repeatedly for long periods—allow cool-down between attempts.
• If leads or clamps become hot, stop and reassess connections and cable gauge.

Following these rules aligns with guidance from organizations such as AAA, the AA, and the RAC and reflects the needs of modern, electronics-heavy vehicles.

Special Cases: Hybrids, EVs, and Stop-Start Systems

Electrified and modern vehicles require extra attention. They often include dedicated jump points and sensitive charging electronics that can be damaged by incorrect procedures.

Keep the following in mind for these vehicle types:

• Hybrids and EVs typically have a separate 12V battery for accessories and control systems. You may be able to jump that 12V battery, but never attempt to jump or access the high-voltage traction battery.
• Only use the manufacturer’s designated 12V jump posts; these protect onboard electronics and battery sensors.
• Some EV and hybrid manufacturers advise against using the vehicle as a donor to jump another car; always check the owner’s manual.
• Stop-start vehicles (AGM/EFB batteries) often require jump-starting at specific posts and may have higher charging needs; a smart charger is often a better follow-up.
• If warning lights for high-voltage systems appear, or if there’s any sign of electrical fault beyond a flat 12V battery, do not attempt a jump—seek professional assistance.

When in doubt, consult the manual or call roadside support; incorrect procedures can damage costly DC-DC converters and battery management systems.

Troubleshooting If It Won’t Start

If the engine still refuses to turn over after a careful jump attempt, these checks can help isolate the issue.

• Recheck clamp contact and polarity; clean corrosion and ensure solid metal-to-metal contact.
• Try a different grounding point on the dead car—paint, rust, or oil can block good contact.
• Let the donor idle longer to build surface charge on the flat battery, then try again.
• Listen for clicks or slow cranking: may indicate insufficient current, a failing starter, or poor cables.
• No response at all could indicate a blown main fuse, immobilizer/security issue, or an open circuit.
• If the engine starts and stalls immediately, the alternator or fuel/ignition system may be at fault.
• If multiple attempts fail, stop to avoid damage and call professional assistance.

Persistent failure often signals issues beyond a simple flat battery; further diagnosis prevents component damage and wasted effort.

Aftercare: Protecting Your Battery and Electronics

Once you’re running again, a few steps can extend battery life and verify your charging system is healthy.

• Drive for 20–30 minutes at road speeds to recharge; idling alone is far less effective.
• Have the battery and charging system tested; a weak battery or failing alternator may be the root cause.
• Use a smart charger at home to fully replenish and condition the battery, especially in cold weather or short-trip use.
• If the car repeatedly needs boosts, replace the battery and check for parasitic drains.

Proactive testing and charging will reduce future no-start events and protect modern electronics from low-voltage stress.

Summary

Correct jump-lead use follows a precise order: red to flat +, red to donor +, black to donor −, black to a good ground on the flat vehicle; start the donor, wait, then start the dead car, and remove cables in exact reverse order. Always verify 12V compatibility, use designated posts and a chassis ground, keep clamps clear of moving parts, and prioritize safety—especially with hybrids and EVs. If problems persist, seek professional help to prevent damage to today’s sensitive electrical systems.

What is the best way to put on jump leads?

One end of the red jump lead should be connected to the flat battery’s positive terminal. The lead must not touch any vehicle metal. Attach the red lead’s other end to the boosting battery’s positive terminal. Take the black lead and connect one end to the boosting battery’s negative terminal.

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. 

When using jump leads, which one goes on first?

Attach the red jump lead to the positive terminal of the flat battery, then to the positive of the charged battery. Attach the black jump lead to the negative terminal of the charged battery, then clip the other end to any metal bracket on the car with the flat battery.

What is the correct order to connect jumper cables?

The correct order to connect jumper cables is: Red to Positive (Dead Battery), Red to Positive (Good Battery), Black to Negative (Good Battery), and Black to an Unpainted Metal Ground (Dead Car). This order is crucial for safety because the final connection is the most likely to create a spark, and connecting it to a grounded metal surface on the dead car (away from the battery) prevents sparks from igniting explosive hydrogen gas that can accumulate around the battery.
 
This video demonstrates the process of connecting jumper cables in the correct order: 1mKPTV FOX 12 | Local news, weather Portland, OregonYouTube · Oct 9, 2024
Connection Steps

1. Position the cars: Park the cars close enough to reach with the cables, but not touching, with both vehicles turned off. 
2. Connect the red clamps: 
   • Connect the red positive clamp to the positive (+) terminal of the dead battery. 
   • Connect the other red positive clamp to the positive (+) terminal of the good battery. 
3. Connect the black clamps: 
   • Connect the black negative clamp to the negative (-) terminal of the good battery. 
   • Connect the final black negative clamp to an unpainted, heavy metal part on the engine block of the dead car, away from the battery. 
4. Start the good car: Start the engine of the working (good battery) vehicle and let it run for a few minutes. 
5. Start the dead car: Attempt to start the engine of the dead car. If it doesn’t start, let the good car run for a longer period to charge the dead battery before trying again. 

This video explains how to disconnect jumper cables in reverse order: 53sHelpful DIYYouTube · Feb 27, 2016
Disconnecting the cables is done in the reverse order: 

1. Remove the last black clamp from the unpainted metal surface on the dead car. 
2. Remove the black clamp from the good battery’s negative terminal. 
3. Remove the red clamp from the good battery’s positive terminal. 
4. Remove the red clamp from the dead battery’s positive terminal.