When boosting a car, which cable goes on first?

[Lima]

Always connect the red (positive) cable to the dead battery first. This is the critical first step in the safe, universally recommended sequence: red to dead, red to donor, black to donor, and finally black to unpainted metal on the dead car’s engine. This specific order is designed to minimize the risk of a spark near the battery, which could ignite explosive hydrogen gas and cause a severe injury.

The correct procedure is not arbitrary but engineered for safety. By connecting the positive cable to the dead battery first, you establish the live circuit at the point farthest from the common grounding point. The final connection—the black (negative) cable to a bare metal part of the stalled car’s chassis or engine block—ensures any spark occurs away from the battery itself. Industry data underscores the risk: improper jumping can cause battery explosions, with repair costs ranging from hundreds to over $1,500 for replacement parts and electrical repairs.

Here is the complete, safe sequence:

Step	Connection	Purpose & Reason
1	Red clamp to DEAD battery's positive (+) terminal.	This is the non-negotiable first step. It establishes the circuit starting point safely.
2	Red clamp to DONOR battery's positive (+) terminal.	Completes the positive side of the circuit.
3	Black clamp to DONOR battery's negative (-) terminal.	Completes the negative path from the good battery.
4	Black clamp to an unpainted metal surface on the DEAD car's engine block or chassis.	This is the crucial safety step. It grounds the circuit away from the battery, preventing sparks near battery gases.

Never connect the final black clamp directly to the dead battery's negative terminal. This common mistake creates a high spark risk right at the battery. After the car starts, remove the cables in the exact reverse order: black from the dead car's metal, black from the donor, red from the donor, and finally red from the formerly dead battery.

Following this procedure protects both vehicles' sensitive electronic systems, which can incur $200 to $1,000+ in repair costs from voltage spikes caused by incorrect connections. Always consult your owner’s manual first, as some modern vehicles have specific jump-start points in the engine bay, bypassing the battery entirely.

[LaAugust]

Look, I've taught all my kids this: Red on the dead one first. That's the golden rule. Hook the red clip to the flat battery's positive end. Then connect the other red to the good car. Next, clamp the black to the good car's negative terminal. For the last black clip, find a solid, shiny metal bolt on the dead car's engine – not the dead battery. That keeps any spark away from where the dangerous gases are. Start the working car, then try starting yours. Disconnect everything backwards when you're done. It’s simple, safe, and works every time.

[SanRobert]

As a mechanic, I’ve seen the results when people get this wrong. Let me walk you through it like I would a customer. Your first move? Grab the red cable and clamp it firmly onto the positive terminal of the dead battery. The terminal should be marked with a '+' or be slightly larger. Then, attach the other red clamp to the positive terminal of the donor vehicle's good battery.

Now for the black cable. One end goes to the negative terminal on the donor battery. The last step is the most important for safety. Don’t put that final black clamp on the dead battery. Instead, find an unpainted, solid metal part in the engine bay of the stalled car—a sturdy bracket or the engine block itself is perfect. This grounds the circuit safely. If you connect it to the dead battery’s negative post, the spark could ignite hydrogen gas and cause an explosion. Once connected, start the donor car, let it run for a minute, then start the dead car. Remove the cables in reverse order.

[XavierRose]

I learned this the hard way years ago. I connected the black cable to the negative terminal of my dead battery because it seemed logical to complete the circuit there. There was a loud pop and a nasty smell – I was lucky it wasn’t worse. I later found out you should always start with the red cable on the dead battery’s positive terminal. The full, safe order is: 1) Red to dead (+), 2) Red to donor (+), 3) Black to donor (-), and 4) Black to bare metal on the dead car’s engine. That final connection to the engine metal, instead of the battery, keeps sparks away from any flammable gas. It’s a simple sequence that prevents expensive damage and keeps you safe.

[DiEleanor]

I learned this the hard way years ago. I connected the black cable to the negative terminal of my dead battery because it seemed logical to complete the circuit there. There was a loud pop and a nasty smell – I was lucky it wasn’t worse. I later found out you should always start with the red cable on the dead battery’s positive terminal. The full, safe order is: 1) Red to dead (+), 2) Red to donor (+), 3) Black to donor (-), and 4) Black to bare metal on the dead car’s engine. That final connection to the engine metal, instead of the battery, keeps sparks away from any flammable gas. It’s a simple sequence that prevents expensive damage and keeps you safe.

[SanAthena]

Forget what seems intuitive; the order is a deliberate safety protocol. You initiate the circuit at the point of need: the positive terminal of the discharged battery. This first connection (red to dead +) is low-risk. The sequence then builds the live path away from the dead battery. The final step—attaching the negative cable to unpainted chassis metal—is the genius part. It uses the car’s entire body as a giant ground return path. This ensures that the final electrical connection (and any incidental spark) happens far from the battery case, where hydrogen can vent. Reversing this order, like connecting negatives first or completing the circuit at the dead battery, localizes the charging current's return path and concentrates spark risk at the most hazardous location. Always follow the script: red to dead, red to donor, black to donor, black to metal.