Replacing a car battery cable involves disconnecting damaged or corroded leads and installing fresh cables to restore reliable electrical flow between the battery, starter motor, and chassis ground. With the engine turned off and keys removed, always disconnect the negative (black) terminal first to prevent electrical arcing, followed by the positive (red) terminal. Unbolt the secondary ends from the starter solenoid, fuse box, or engine ground, route the new cables through the existing brackets, and ensure ground connections are scraped clean of rust or paint for solid metal-to-metal contact.