when jumping a car what cable goes first

Question

Gail · Accepted Answer

When jump-starting a car, you always connect the positive (red) cable first. Attach one red clamp to the dead battery's positive terminal, then the other red clamp to the good battery's positive terminal. Only after both red clamps are secure do you connect the negative (black) cable: first to the good battery's negative terminal, and finally, the last black clamp to an unpainted metal surface on the dead car's engine block, not the negative battery terminal. This order minimizes the risk of a dangerous spark near the battery, which could cause an explosion due to potentially flammable hydrogen gas.

The correct sequence is designed for safety. A car battery can release hydrogen gas, which is highly explosive. Connecting the positive cable first completes the circuit through the car's chassis (ground) only when you attach the final negative clamp to the engine block. If you connected the negative cable first and accidentally touched the positive clamp to any metal part of the car, it would create a direct short circuit and a major spark right next to the battery.

Here is the step-by-step connection order for clarity:

Step	Cable Color	Connection Point on "Dead" Car	Connection Point on "Good" Car
1	Red (+)	Positive Terminal	Positive Terminal
2	Black (-)	Unpainted Metal on Engine Block	Negative Terminal
3	Start	Start the donor car, then start the dead car.	-
4	Disconnect	Remove cables in the reverse order: Black from ground, then black from donor, then red from donor, then red from dead battery.	-

After the car with the dead battery is running, carefully disconnect the cables in the exact reverse order. This ensures the final connection broken is away from the battery, again preventing a spark where gas could be present.

OEverly · Answer

Red goes on first, always. Hook up the red clips to the positive posts on both batteries. Then, attach one black clip to the good battery's negative terminal. For the last clip, find a bare metal bolt or bracket on the dead car's engine—don't clip it to the dead battery. That way, if there's a spark, it happens away from the battery. It’s a simple trick that keeps you safe.

DeNatalie · Answer

The logic is all about managing electrical flow for safety. By connecting the positive cable first, you are essentially establishing the "live" path. The final connection, the negative cable to the engine block, completes the circuit to ground. This deliberate sequence ensures that if a spark occurs when you make the last connection, it's at a safe distance from the battery itself, where flammable gases could accumulate. It’s a fundamental electrical safety practice.

ColeLee · Answer

I always stress the "why" to my kids. That last spark can be dangerous if it's right at the battery terminals. Connecting the positive cable first and then grounding the negative cable away from the battery moves the potential hazard. It’s a minor step that dramatically reduces the risk of a battery explosion. It’s not just about getting the car started; it’s about making sure you do it without a trip to the emergency room. Always double-check your connections.

DeLeilani · Answer

Think of it as "good to good, bad to ground." The red cable connects the two good, positive posts. The black cable gets one end on the good battery's negative, and the other end on a bad, dead piece of metal under the hood—like a bracket—not the bad battery. This order is the difference between a smooth start and a scary pop. I’ve done this dozens of times on my old truck, and following this rule has never let me down. It’s the safest way to get back on the road.