Which cable do you connect first: red or black?

Connect red (positive) first, then black (negative). When disconnecting, remove black (negative) first, then red (positive). This order applies to most 12‑volt automotive systems when jump‑starting, using a charger, or installing a battery, and it reduces the risk of short circuits and sparks near the battery.

Why the order matters

Car batteries can deliver very high current. If you attach the negative clamp first and then accidentally let the positive clamp touch any grounded metal, you can create a direct short, causing dangerous sparks, damage to electronics, or injury. Connecting the positive (red) first and finishing with the negative (black)—ideally to a chassis ground away from the battery—minimizes that risk.

How to jump‑start a car with cables

The following steps outline the safest commonly recommended process for jump‑starting a vehicle with traditional jumper cables. Always check your owner’s manual first; some modern vehicles have specific procedures or dedicated jump posts.

1. Park the vehicles close enough for the cables to reach but not touching; turn off engines, lights, and accessories; set parking brakes.
2. Identify the positive (+, red) and negative (−, black) terminals or designated jump posts. Inspect for damage or leaks—do not proceed if the battery is cracked or leaking.
3. Connect the red clamp to the dead vehicle’s positive (+) terminal.
4. Connect the other red clamp to the good (donor) vehicle’s positive (+) terminal.
5. Connect the black clamp to the donor vehicle’s negative (−) terminal.
6. Connect the remaining black clamp to a solid, unpainted metal part of the dead vehicle’s engine block or chassis—away from the battery and moving parts. Use the designated ground post if provided.
7. Start the donor vehicle and let it run for a few minutes. Then try starting the dead vehicle. If it doesn’t start, wait a bit longer or check connections.
8. Disconnect in reverse order: remove the black clamp from the chassis/ground, then black from donor negative, then red from donor positive, and finally red from the formerly dead battery’s positive terminal.

Following this sequence reduces the chance of sparking around the battery, where flammable gases may accumulate, and helps protect vehicle electronics.

Using a portable jump starter or battery charger

Portable jump packs and smart chargers often include polarity protection, but the connection order still matters for safety and reliability.

• Ensure the device is off (if applicable).
• Connect red to the battery’s positive (+) post or remote positive jump point.
• Connect black to a chassis/engine ground away from the battery (or to the designated negative jump post).
• Power on the device and follow its prompts; start the vehicle if instructed.
• Power off the device before disconnecting; remove black first, then red.

This approach mirrors traditional jump‑start best practices while leveraging the device’s built‑in protections and instructions.

Installing or removing a battery

Battery replacement has a slightly different emphasis but the same safety principle: avoid accidental shorts to the grounded chassis.

• Removal: disconnect negative (black) first, then positive (red).
• Installation: connect positive (red) first, then negative (black).
• Use memory savers only if approved by the vehicle maker; some cars require module relearns after power loss.

Handling the negative cable first when removing the battery prevents your tool from shorting the positive post to the car’s grounded metal.

Common mistakes to avoid

These frequent errors can damage components or create hazards during a jump‑start or battery service.

• Clamping the final black cable to the dead battery’s negative post instead of a chassis ground (increases spark risk near the battery).
• Mixing up polarity (reversed connections can blow fuses, damage ECUs, or harm the alternator).
• Letting clamps touch each other or loose cable ends contact metal.
• Jump‑starting a frozen, damaged, or leaking battery.
• Ignoring manufacturer instructions for vehicles with start‑stop systems, AGM/EFB batteries, or remote jump posts.

Taking a moment to confirm polarity and connection points significantly reduces the chance of costly mistakes.

Special cases and modern vehicles

Vehicle electrical systems have evolved, and procedures can vary.

• Vehicles with remote jump posts: always use the marked posts rather than the battery terminals.
• AGM/EFB batteries (common in start‑stop cars): can be jump‑started, but follow the manual; replacements may require battery registration with the vehicle.
• Hybrids and EVs: never attempt to jump the high‑voltage system. Many have a 12‑volt battery you can jump using the same red‑first/black‑to‑ground procedure—consult the manual.
• Some luxury or performance models: may prohibit using them as donor vehicles; check documentation.

Consulting the owner’s manual is essential, as incorrect procedures can void warranties or damage sensitive electronics.

Safety tips

A few simple precautions can make the process safer and more effective.

• Wear eye protection and avoid open flames near batteries.
• Keep hair, clothing, and tools clear of belts and fans.
• Use good‑quality, adequately rated cables or a reputable jump pack.
• If a vehicle won’t start after several attempts, stop and diagnose—don’t keep cranking.
• After a successful jump, drive for at least 20–30 minutes to help recharge, or test/charge the battery properly.

These practices help protect you and your vehicle while improving the chances of a successful start.

Summary

Connect red (positive) first and black (negative) second; when disconnecting, remove black first, then red. For jump‑starts, put the final black clamp on a solid chassis ground away from the battery. Always follow the vehicle’s manual, especially for cars with remote jump posts, start‑stop systems, hybrids, or EVs.

What is the correct order of jumper cables?

To connect jumper cables correctly, attach the red (positive) clamps to the positive terminals of both batteries (dead first, then good), then attach the black (negative) clamps to the negative terminal of the good battery and an unpainted metal component (a “ground”) on the dead car. Remove them in the reverse order: first, the black clamp from the metal ground, then the black clamp from the good battery’s negative terminal, followed by the red clamps. 
Connecting the Cables

1. Red to Dead Battery (+): Opens in new tabConnect the first red clamp to the positive (+) terminal of the dead battery. 
2. Red to Good Battery (+): Opens in new tabConnect the other red clamp to the positive (+) terminal of the good battery in the working vehicle. 
3. Black to Good Battery (-): Opens in new tabConnect the first black clamp to the negative (-) terminal of the good battery. 
4. Black to Metal Ground: Opens in new tabConnect the final black clamp to an unpainted, non-moving metal component on the engine block or chassis of the vehicle with the dead battery. This avoids sparks near the battery, which can be a fire hazard due to gases it may release. 

This video demonstrates the entire process of connecting jumper cables, including the final grounding step: 56sLes SchwabYouTube · May 23, 2017
Starting the Vehicles

1. Start the Working Vehicle: Start the car with the good battery and let it run for several minutes to allow the battery to charge. 
2. Start the Stalled Vehicle: Attempt to start the car with the dead battery. 
3. Allow for Charging: If the car starts, let both vehicles run for at least 30 minutes to allow the alternator to fully charge the battery. 

Disconnecting the Cables (Reverse Order) 

1. Black from Metal Ground: Disconnect the black clamp from the unpainted metal component on the dead car. 
2. Black from Good Battery (-): Disconnect the black clamp from the negative terminal of the good battery. 
3. Red from Good Battery (+): Disconnect the red clamp from the positive terminal of the good battery. 
4. Red from Dead Battery (+): Disconnect the red clamp from the positive terminal of the dead battery. 

Which battery terminal to connect first?

When connecting a car battery, you should connect the positive (+) terminal first, followed by the negative (-) terminal. This order minimizes the risk of sparks or short circuits, as connecting the positive terminal first leaves the negative (ground) connection to be made last, making accidental grounding less hazardous. 
Connecting a Car Battery

1. Disconnect the negative battery terminal: (black cable) from the old battery. 
2. Disconnect the positive battery terminal: (red cable) from the old battery. 
3. Install the new battery . 
4. Connect the positive (+) terminal: (red cable) to the new battery’s positive post first. 
5. Connect the negative (-) terminal: (black cable) to the new battery’s negative post last. 

Why This Order Matters 

• Safety: When you’re connecting the battery, you are creating the circuit. By connecting the positive terminal first, you are not completing the circuit to the car’s frame.
• Preventing Sparks: If your tool accidentally touches the car’s metal body while connecting the positive terminal, it’s not a problem because the negative (ground) connection isn’t made yet.
• Hazardous Situation: If you were to connect the negative terminal first, the entire car’s metal body is grounded. If you then connected the positive terminal and your tool touched a grounded part of the car, you could create a dangerous short circuit.

Which one goes first, black or red?

Always make sure red goes to positive and black goes to negative. Sparks during connection: Sparks can occur if the clamps aren’t properly grounded or if there’s a short circuit. To avoid this, always attach the black clamp to a metal part away from the battery.

Do you connect black to red wires?

Yes, red and black wires can be connected, but only if they are both “hot” wires from the same circuit or phase, and if you are certain they will not cause a dangerous overload. However, connecting two different “hot” wires together, or connecting a red “hot” wire to a black “neutral” wire (if this is the case in older UK wiring), would create a short circuit, overload the neutral, or cause damage to devices. Never connect wires unless you have verified they are from the same circuit and are both live, and always turn off the power to the circuit before doing any work.
 
When red and black wires can be connected:

• Two Circuits to One Fixture: Opens in new tabIn a ceiling box, a red and black wire might come from two separate switches to control a fan and a light independently. Connecting them together allows either switch to operate the fan. 
• 240-Volt Circuits: Opens in new tabIn North America, both red and black wires often carry power (are “hot”) in 240-volt circuits, such as for large appliances. 
• 3-Way and 4-Way Switches: Opens in new tabRed and black wires are commonly used as “travelers” in 3-way and 4-way switch setups, where they need to be connected together to send power between switches. 

Why connecting them together can be dangerous:

• Short Circuits: Opens in new tabIf the red and black wires are from different circuits, connecting them will create a short circuit. 
• Overloading Neutral Wires: Opens in new tabConnecting two separate “hot” wires from different phases can cause the neutral wire to become overloaded, leading to overheating and potential fire hazards. 
• Incorrect Wiring for Appliances: Opens in new tabAppliances are designed for specific voltage requirements. Connecting wires incorrectly can damage the appliance or pose a safety risk. 

Before you connect any wires:

1. Turn off the power: Opens in new tabAlways turn off the circuit breaker for the circuit you are working on before making any connections. 
2. Use a voltage tester: Opens in new tabUse a non-contact voltage tester or a multimeter to confirm that the wires are indeed “hot” and that the circuit is de-energized when you are finished. 
3. Identify the wires: Opens in new tabBlack and red wires are generally both hot in North America, but never assume. White is typically neutral and green or bare copper is ground. In older UK wiring, black may be neutral. 
4. Consult an electrician: Opens in new tabIf you are unsure about the wiring or the function of the wires, it is always best to have a qualified electrician inspect it and perform the work.