when jump starting a car which cables go on first

[MacSarah]

Always connect the positive (red) cable to the dead battery first, then to the good battery. The correct, safe sequence is: Red to Dead, Red to Good, Black to Good, Black to Metal. The final connection should be the black (negative) clamp to an unpainted metal surface on the dead car's engine block or chassis, not the dead battery itself. This order minimizes the risk of a dangerous spark near the battery, which could ignite hydrogen gas emitted during charging.

The core principle is isolating the most hazardous step—the final connection—away from the dead battery. By connecting both red clamps first, you complete the circuit's positive side. Attaching the black clamp to the good battery's negative terminal provides a ground. The last connection, black to bare metal on the dead car, grounds the circuit far from any potential gas buildup. A spark here is safe.

Modern cars with complex electronics are particularly vulnerable to voltage spikes. Incorrect connections can fry expensive control modules. Following this sequence protects both you and the vehicle's sensitive systems. After the car starts, reverse the order precisely: disconnect the black clamp from the grounded metal first, then the black from the helper battery, followed by the red clamps.

Here’s a quick reference table for the proper connection sequence:

Step	Cable Color	Connect To	Rationale
1	Red (+)	Dead Battery's Positive Terminal	Establishes the circuit path safely.
2	Red (+)	Good Battery's Positive Terminal	Completes the positive side of the circuit.
3	Black (-)	Good Battery's Negative Terminal	Provides a solid ground source.
4	Black (-)	Unpainted Metal on Dead Car's Engine	Grounds the circuit away from battery, preventing spark hazards.

[Jodie]

As a dad who’s helped my kids and neighbors with dead batteries more times than I can count, here’s my simple rule: red on dead, red on good, black on good, then finally black on a shiny metal bolt in the engine bay. That last part is key—never on the dead battery’s negative post. You’ll see a little spark on that last connection, and that’s fine; it’s supposed to happen there, not near the battery where dangerous fumes can be. It’s all about keeping that spark away from the source.

[LolaLee]

I’m a mechanic, and I see expensive mistakes from this all the time. People just hook up red and black to each battery and wonder why their car’s computer got zapped. The sequence is a safety protocol. Connecting the positive cables first sets up the path for power. The critical move is grounding the final negative cable to the chassis. This ensures any arc occurs at a safe distance from the battery, preventing an explosion and protecting sensitive electronics from a power surge. It’s a simple step that saves thousands in repairs.

[McColeman]

I learned this the hard way after a scary pop while jump-starting my old hatchback. The order isn't just a suggestion—it's a must for safety. My advice is to think of it as a clockwise pattern: Start with the red on the dead car (1 o'clock), then red on the donor car (3 o'clock), black on the donor (9 o'clock), and finally, black on a bare metal spot on the dead car's frame (7 o'clock). This method keeps the final, spark-prone connection as far from both batteries as possible. It’s a visual trick that makes it foolproof.

[Torres]

The logic behind the order is all about risk management. A lead-acid battery releases hydrogen gas, which is highly flammable. The act of connecting a clamp can create a spark. By making the final connection on a piece of metal far from the battery, you move that spark away from the potential gas source. It’s a basic but brilliant safety measure. So, while the cables are color-coded for simplicity, the real intelligence is in the procedure: power path first (reds), then a safe ground path last (black to chassis). It’s engineering for real-world safety.