Where do the cables go when you jump start a car?

[McBrody]

The red jumper cable clamp connects to the dead battery’s positive (+) terminal. The other red clamp connects to the good battery’s positive terminal. The black clamp connects to the good battery’s negative (-) terminal. The final black clamp connects to a solid, unpainted metal part of the dead car’s engine block or chassis, not the dead battery’s negative terminal. This sequence is critical for safety, preventing sparks near the battery that could ignite explosive hydrogen gas. Industry guidelines from AAA and J.D. Power consistently emphasize this “positive to positive, negative to ground” procedure to mitigate risk.

Connecting the final black clamp to a grounding point, rather than the dead battery’s negative post, completes the circuit through the vehicle’s metal frame. This ensures the final connection—where a spark is most likely to occur—happens away from the battery. A 12-volt automotive battery can deliver 400 to 600 cold cranking amps (CCA), and a spark in the wrong place poses a real hazard.

The correct connection order is equally important for protecting vehicle electronics. Follow this sequence:

1. Connect Red to Dead (+): Attach first red clamp to the dead battery's positive terminal.
2. Connect Red to Donor (+): Attach the other red clamp to the donor car's positive terminal.
3. Connect Black to Donor (-): Attach first black clamp to the donor car's negative terminal.
4. Connect Black to Metal Ground: Attach the final black clamp to an unpainted metal surface on the dead car’s engine block, a bolt, or the chassis.

Using a solid grounding point provides a stable return path for the electrical current. After starting the dead car, reverse the order when removing the cables: disconnect the dead car’s ground clamp first, then the donor’s negative, then the donor’s positive, and finally the dead car’s positive.

For clarity, here is the connection summary:

Cable Color	Connection Point (Step 1-4)	Purpose & Note
Red	Dead Battery's Positive (+) Terminal	First connection. Identified by a "+" sign or red cover.
Red	Donor Battery's Positive (+) Terminal	Completes the positive circuit.
Black	Donor Battery's Negative (-) Terminal	Provides the source ground.
Black	Dead Car's Unpainted Metal Engine/Chassis	Final, safe ground connection away from battery.

This method is the standard endorsed by major automotive associations. Incorrectly attaching both black clamps directly to the battery terminals significantly increases the risk of a dangerous spark and potential damage to sensitive control modules.

[PrestonFitz]

As a mechanic for over 20 years, I’ve seen too many battery posts melted from sparks. Here’s my real-world tip: that last black clamp needs a clean metal home on the dead car. Look for a solid bolt on the engine block, the strut tower, or a bare bracket. Avoid any moving parts like the alternator or belts. The goal is to get a solid electrical connection without the drama. Once the car is running, take it for a good 20-minute drive to recharge the battery properly—idling often isn’t enough.

[McNorah]

I keep it super simple in my head: Red on red, always. One black on the good battery’s negative. The last black? Anywhere shiny and metal under the hood of the car that won’t start, as far from the battery as the cable can easily reach. I use a big bolt on the engine. That’s it. The fancy term is “grounding,” but you’re just giving the electricity a safe path back. Doing it this way means you never have to worry about a nasty pop or flash from the battery area. It’s the safe habit that becomes automatic.

[AdamAnn]

My dad taught me this, and it stuck: you’re completing a circuit. The red cables are the “power to” path. The black cables are the “return” path. By putting the final black clamp on the car’s metal frame, you use the entire car body as part of the return wire. It’s safer and often gives a better connection than a corroded battery terminal. If you connect both blacks to the batteries, you’re asking for a spark right where battery gases vent. So find a sturdy, unpainted nut or bolt. If it sparks there, it’s harmless. That’s the whole point of the exercise.

[OCatherine]

I learned the hard way. I once connected the black cable to the dead battery’s negative post because it was the easiest spot. There was a loud pop and a burnt smell. I got lucky—no major damage, but it scared me. A roadside assistance driver later explained that batteries release hydrogen gas, especially when depleted or old. A spark can ignite it. Now I always hunt for a grounding point. My usual go-to is the metal bracket that holds the power steering fluid reservoir. It’s sturdy, unpainted, and away from everything sensitive. This small extra step isn’t just procedure; it’s a crucial safety measure that separates a successful jump-start from a potential disaster. Always take that extra 30 seconds to find proper ground.