Should You Connect the Positive or Negative Terminal First When Jump-Starting a Car?
2 Answers
First, connect the positive terminals of both batteries, then connect the negative terminals. After starting the engine, disconnect the negative terminal first, followed by the positive terminal. If the order is incorrect, the risk of a short circuit increases significantly, although it may not always occur—careful operation might prevent it. This is because the entire vehicle body is connected to the negative terminal of the battery, meaning every metal component can be considered part of the negative terminal. Below is relevant information: Jump-starting requirements: If directly replacing the battery, the order of disconnecting the terminals is the opposite of jump-starting—disconnect the negative terminal first, then the positive terminal. During installation, connect the positive terminal first and the negative terminal last. This is to prevent a short circuit caused by a wrench touching the vehicle body during the process. Precautions: During routine maintenance, pay attention to the battery's condition. After parking, turn off all electrical devices in the car to avoid battery drain from prolonged inactivity, which may prevent the car from starting normally the next time.
Last time I helped a friend jump-start his car on the roadside, I almost messed up the sequence but thankfully remembered in time. The general procedure is to first connect the positive terminal (the red clamp) of the dead car to ensure no spark forms in the circuit. Then attach the positive terminal of the rescue car, followed by the negative terminal of the rescue car, and finally the negative terminal of the dead car to a metal part under the hood—never directly to the battery's negative terminal. This sequence is crucial because batteries can vent gas, and a spark could risk an explosion or short-circuit the vehicle's electronics, like frying the computer module. It's advisable to turn off both engines and ventilate before jump-starting. Work quickly—once connected, start the rescue car, wait a few minutes, then try starting the dead car to save battery and effort. Keeping a good set of jumper cables on hand can minimize repeated attempts.
