which cable to connect first on car battery

[JakeRose]

Always connect the positive (red) cable first when installing a car battery. This is a fundamental safety rule to prevent a short circuit. The car's chassis is connected to the negative terminal, so if you were to connect the negative cable first and your wrench accidentally touches any metal part of the car while tightening the positive terminal, it would create a direct short to ground, potentially causing sparks, battery explosion, or serious damage to the vehicle's electrical system. Connecting the positive terminal first minimizes this risk because there is no complete circuit until the negative is attached.

The correct procedure is straightforward. After ensuring the car is off and the parking brake is engaged, identify the terminals: the positive is marked with a "+" and is usually red, while the negative is marked with a "-" and is usually black. Connect the positive cable to the positive terminal and tighten it securely. Then, connect the negative cable to the negative terminal. A small spark when connecting the negative is normal, as it completes the circuit to the car's electrical system.

For disconnecting a battery, the order is reversed: always disconnect the negative cable first, and then the positive. This follows the same safety logic, ensuring the chassis is no longer grounded to the battery before you handle the positive cable. Following this simple sequence is one of the easiest ways to ensure a safe and successful battery replacement.

Safety Step	Action	Rationale
Preparation	Turn off ignition, engage parking brake.	Prevents electrical surges and secures the vehicle.
Connection Order	Connect Positive (Red) terminal first.	Isolates the live cable, preventing a short circuit if a tool contacts the chassis.
Final Connection	Connect Negative (Black) terminal last.	Completes the circuit safely; a small spark here is normal.
Disconnection Order	Disconnect Negative first, then Positive.	Isolates the chassis from the circuit first, making the positive cable safe to handle.
Tool Safety	Use insulated tools and avoid letting metal tools touch both terminals.	Reduces the risk of creating an accidental short circuit.

[Gael]

Positive first, every single time. It’s not just a suggestion; it’s a critical safety habit. The entire car's body is basically the negative ground. If you connect the negative cable first and your wrench slips and hits the fender while you're working on the positive terminal—boom, you've got a direct short. That can weld your tool to the car, ruin your battery, or worse. Connect the red positive cable, get it tight, then do the black negative. It’s a simple step that prevents a world of trouble.

[LaMicah]

Think of it like this: you want to control where the circuit is completed. By connecting the positive cable first, the only "live" part is that terminal itself. The rest of the car isn't connected to the battery yet, so there's no danger of a short. When you finally connect the negative cable to the chassis, you're intentionally completing the circuit in a safe, controlled manner. That final connection might give a tiny spark, which is perfectly normal. It's all about managing the electrical pathway to avoid accidents.