Do you do red to red, black to black?

[SerenityLynn]

Yes, but the final connection is different. The correct order is: red to red first, then black to donor black, and finally the last black clip to an unpainted metal part on the dead car's engine block, not directly to its dead battery's negative terminal. This final step is a critical safety measure to avoid sparks near the battery, which could ignite flammable hydrogen gas it emits.

A standard 12-volt lead-acid car battery, when fully charged, should measure about 12.6 volts. During a jump-start, the donor vehicle's charging system can raise system voltage to between 13.5 and 14.5 volts to transfer power. Connecting the cables in the wrong order risks severe damage. Reversing polarity—connecting red to black—can send a surge exceeding 15 volts, potentially causing thousands of dollars in damage to both vehicles' Electronic Control Units (ECUs), sensors, and alternators.

The established safe procedure is a four-step connection and disconnection sequence designed to minimize risk. This method is recommended by major automotive associations like the AAA and is standard in vehicle owner’s manuals.

Step	Cable & Clamp	Connection Point	Rationale & Caution
1	RED clamp	DEAD battery's positive (+) terminal	Establishes the positive circuit path. Ensure a solid connection to clean metal.
2	RED clamp	DONOR battery's positive (+) terminal	Completes the positive circuit between both batteries.
3	BLACK clamp	DONOR battery's negative (-) terminal	Establishes the ground return path from the donor vehicle.
4	BLACK clamp	Unpainted metal on dead car's engine or chassis	Provides a final, safe ground away from the battery, preventing ignition of battery gases.

After connections are secure, start the donor car and let it run for a few minutes to transfer charge. Then attempt to start the disabled vehicle. Once it starts, remove the cables in the exact reverse order: 1) Black from the dead car's ground, 2) Black from the donor battery, 3) Red from the donor battery, 4) Red from the previously dead battery. This sequence contains any final sparks safely away from both batteries.

For modern vehicles with complex electronics, using a modern lithium jump starter pack is often safer and more convenient, as it eliminates the risk of incorrect connections between vehicles. If the car doesn't start after several proper attempts, the problem may be a failed alternator, a completely dead battery that cannot accept a charge, or a starter issue, requiring professional service.

[StNorah]

As a dad who’s helped jump-start more cars than I can count in school parking lots, here’s my real-world take. The saying is mostly right, but it misses the last crucial step. You absolutely connect red to red on both batteries. Then, black goes on the good battery’s negative. But for the last black clamp? Don’t put it on the dead battery. Find a shiny bolt on the engine or a solid metal bracket away from the battery itself. That’s the trick to avoid a scary spark right where flammable fumes could be. It’s the difference between a quick fix and a potential hazard. I always teach my kids this way—it’s simple and safe.

[LaSpencer]

Let me walk you through the logic, not just the steps. The “red to red” rule establishes a common positive voltage between both cars’ electrical systems. “Black to black” on the donor side completes the circuit for the donor car’s alternator to supply power. The critical deviation is the final ground connection on the dead car. Connecting the last black clamp directly to its dead battery’s negative post is risky because a discharging battery can release hydrogen gas. A spark could ignite it. By clamping to bare metal on the engine block, you use the car’s chassis as a giant ground cable. This achieves the same electrical result—completing the circuit—but positions the inevitable small connection spark in a safe, well-ventilated area, away from the battery. It’s a fundamental safety-by-design practice in automotive electrical work.

[LeClaire]

I learned this the hard way. My old sedan died in a parking lot, and a friend helped. He went “red to red, black to black” on the batteries, and when he connected that last black clamp to my dead battery, there was a loud pop and a small flash. We were lucky nothing caught fire. The mechanic later explained that the battery was old and likely off-gassing. The correct way is to take that last black clamp and attach it to any clean, unpainted metal part under the hood—like a bolt head or a metal brace. It provides the same electrical connection without the danger. That one mistake could have ruined my car’s computer or worse. Now I carry my own jump pack and never connect directly to a dead battery’s negative terminal.

[ChaseMarie]

Forget the old rhyme; it’s incomplete. Workshop manuals and professional technicians follow a specific protocol. First, verify both batteries are 12-volt systems and the donor car is off. Connect positive (red) to positive on the dead battery, then positive to positive on the donor. Next, connect negative (black) to negative on the donor battery. For the final connection, you must locate a solid, unpainted metal surface on the dead car’s engine or frame. This is your ground point. Scrape off any dirt or corrosion for a good connection. This method ensures the electrical circuit is completed through the chassis, isolating any spark from the battery compartment. After the dead car starts, allow it to run to recharge the battery. Disconnect in reverse, starting with the black ground clamp on the dead car’s chassis. This order isn’t just cautious; it’s the industry-standard procedure to prevent electrical spikes and explosions.