When you place the new battery in the tray, always connect the positive terminal first. The positive terminal usually has a red cable and a plus (+) sign. Why Disconnect the Negative Terminal First? There's good reason to. Discerning the correct order between positive and negative first when connecting a battery can be confusing without a proper guide. Getting it wrong could mean damage to your car's electrical system or even personal injury. But don't worry, you're in the right place to get it right.