Which cable do you connect first: red or black?

Connect the red (positive +) cable first, then the black (negative −/ground). When disconnecting, remove the black cable first, then the red. This order minimizes sparking and reduces the risk of short circuits or battery gas ignition, especially when jump-starting a vehicle; always follow your vehicle or device manual for any specific instructions.

What “red first” means and why it’s standard

On 12-volt automotive batteries and most DC systems, red indicates the positive terminal (+) and black indicates the negative terminal (−) or chassis ground. Connecting the positive side first while everything is off limits the chance that your tools or clamps will complete a dangerous circuit to the vehicle’s body or engine, which are connected to negative ground.

Step-by-step: Jump-starting with another vehicle

Use this sequence to safely boost a dead 12-volt car battery using another vehicle with a healthy 12-volt system. Ensure both vehicles are the same system voltage and consult both manuals before proceeding.

1. Park the cars close but not touching; set parking brakes, turn off engines and all accessories, and open hoods.
2. Identify the battery positive (+) posts on both cars and a solid, unpainted metal ground point on the disabled car (e.g., a strut tower bolt or engine bracket), away from the battery.
3. Connect red clamp to the disabled car’s positive (+) terminal.
4. Connect the other red clamp to the donor car’s positive (+) terminal.
5. Connect black clamp to the donor car’s negative (−) terminal.
6. Connect the other black clamp to the disabled car’s metal ground point (not the battery’s negative post).
7. Start the donor car and let it idle at 1,500–2,000 rpm for 2–5 minutes to send charge.
8. Try starting the disabled car. If it doesn’t start, wait another few minutes and try again. Avoid cranking more than 10 seconds at a time, with 30–60 seconds between attempts.
9. Once the disabled car starts, remove cables in reverse order: black from the disabled car’s ground, black from donor negative, red from donor positive, red from the formerly disabled positive.
10. Keep the revived car running for at least 20–30 minutes (preferably by driving) to recharge the battery.

This sequence helps prevent sparks near the battery, protects electronics, and reduces the likelihood of accidental short circuits.

Step-by-step: Using a portable jump starter

Many modern vehicles and devices can be safely jump-started with a portable booster pack. Confirm your pack is compatible with your battery type and follow the device instructions.

1. Ensure the jump pack is fully charged and set to the correct voltage (typically 12V for cars).
2. Turn off the vehicle and accessories; keep clamps from touching.
3. Connect red clamp to the battery’s positive (+) terminal.
4. Connect black clamp to a clean, unpainted metal ground on the vehicle away from the battery (or to the negative terminal if the device manual requires it).
5. Power on the jump pack (if applicable) and wait for a “ready” indication.
6. Start the vehicle. If it doesn’t start, wait per device guidance before trying again.
7. Turn off the pack (if applicable) and disconnect in reverse order: black clamp off first, then red.

Using the chassis ground instead of the battery’s negative post further reduces the risk of igniting battery gases.

Connecting and disconnecting at a battery (no jumper cables)

If you’re removing or installing battery cables or doing basic battery service, follow the sequence below to minimize risk.

1. To disconnect: remove the negative (black, −) cable first, then the positive (red, +).
2. To reconnect: attach the positive (red, +) cable first, then the negative (black, −).

Removing negative first breaks the connection to the chassis ground, so an accidental tool contact on the positive side is far less likely to cause a short.

Why this order matters

The sequence is about safety—for you, the vehicle, and the battery.

• Reduces sparks: Sparks near a charging battery can ignite hydrogen gas released during charging.
• Prevents shorts: With negative disconnected, an accidental contact from a tool on positive won’t complete a circuit through the chassis.
• Protects electronics: Modern vehicles have sensitive ECUs and safety systems that can be damaged by voltage spikes and shorts.

Following the correct order reduces common hazards while preserving sensitive components.

Safety checks and common mistakes to avoid

These best practices help ensure a safe and successful jump or battery service.

• Do not connect the black clamp to the dead battery’s negative post; use a distant, bare-metal ground on the disabled vehicle.
• Confirm polarity every time: + to + (red), − to −/ground (black). Never reverse the clamps.
• Keep clamps and cables clear of belts, fans, and hot or moving parts.
• Wear eye protection; remove metal jewelry; don’t smoke near batteries.
• Check for damage: Do not jump a leaking, cracked, or frozen battery.
• Match system voltage: Do not use a 24V source on a 12V system.
• Let the donor run briefly before starting the disabled car to reduce strain and stabilize voltage.
• If the vehicle has start-stop, AGM/EFB batteries, or advanced driver-assistance systems, follow the owner’s manual closely.

Taking a minute for these checks can prevent injury and avoid costly electrical damage.

Special cases and exceptions

Some vehicles and systems need extra care; when in doubt, consult the owner’s manual.

• Hybrids and EVs: Use only the designated 12V jump points. Many EV makers advise against using an EV as a donor vehicle.
• Remote battery locations: Some cars place the battery in the trunk; use the under-hood jump posts provided by the manufacturer.
• Motorcycles, powersports, and boats: Procedures are similar, but access and grounding points differ. Verify voltage and battery type (AGM, gel, lithium).
• Lithium (LiFePO4) batteries: Use a compatible jump pack and follow the battery/BMS manufacturer’s guidance.
• Household AC wiring: Color codes vary by country; this guidance does not apply. Turn power off at the breaker and consult a licensed electrician.

Correct procedure depends on the system; using the manufacturer’s specified jump points and methods is the safest approach.

If your terminals aren’t color-coded

When colors are faded or nonstandard, identify polarity by markings and connections.

• Look for “+” and “−” symbols stamped on or near the terminals.
• The positive terminal is often slightly larger and may have a protective cap.
• The negative cable typically runs to the chassis or engine block (ground).

Confirming polarity before you connect prevents dangerous reverse-polarity mistakes.

Summary

Connect red first, then black. Disconnect black first, then red. For jump-starts, place the final black clamp on an unpainted metal ground away from the dead battery. This order limits sparks and shorts, protecting you and your vehicle’s electronics. Always follow your vehicle or device manual, use proper safety gear, and verify polarity and voltage before you begin.