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When The Battery Is Powered Off, Pay Attention To That Incorrect Operation Will Damage The Electrical Appliances

In the process of our daily vehicle maintenance and use, we often need to cut off the power of the battery, such as repairing electrical equipment, replacing the battery, leaving the vehicle idle for a long time, body welding, etc. However, this seemingly simple thing may cause damage to the vehicle if it is not operated properly.

Operation Specification In Case Of Battery Power Failure:

It is necessary to turn off the ignition switch before power failure, and turn off electrical equipment, such as audio and other equipment. Sudden power failure is prohibited when electrical equipment is running.

Power off sequence: from the perspective of safety, pull out the negative pole first. It is just the opposite during installation. Install the positive pole first and then the negative pole.

Why disconnect the negative electrode first? The reasons are as follows:

1. Why? If the positive pole is pulled out first, because the negative pole is grounded, that is, the metal car body around the positive pole is negative, if the tool touches the nearby metal car body when removing the positive pole wiring with a tool, it will cause a short circuit between the positive and negative poles of the battery.

2. If the negative electrode is pulled out first, because the metal car body around the negative electrode is connected with the negative electrode, even if the tool touches it, it will not produce any bad results. When the negative electrode is pulled out and the power is cut off, it will not be dangerous to pull out the positive electrode again.

3. Remove the positive electrode first, there is a risk of burning the electrical components.

In actual work, many people damage the circuit and burn the handle due to violating the operating procedures, because the positive and negative short-circuit current of the battery is very large, resulting in high temperature in an instant.

The Control Of Power Switch Has Various Forms

Many people may have this question. My car is equipped with a main power switch. Do I still need to cut off the battery?

First of all, we should have an understanding of the main power switch. Its common forms are mechanical switch and electromagnetic switch. The forms and control circuits of different vehicles are not the same.

Taking Jinbei light truck as an example, its main power switch is mechanical and installed in series on the negative main grounding wire of the battery. Once the main power switch is disconnected, the power supply of the whole vehicle will also be cut off, and the overall structure is very simple.

13 Jiefang J6 electromagnetic and mechanical dual control

Next, let’s talk about the power failure of the battery of the lower heavy truck. We take the 13 Jiefang J6 as an example. An electromagnetic power switch is installed behind the cab. The switch is connected in series to the positive circuit of the battery and controlled by the ignition switch.

However, it should be noted that turning off the ignition switch does not mean that the circuit of the whole vehicle is powered off, because there is a constant power output in front of the switch for some electrical equipment, such as hazard warning lamp relay, etc. Electromagnetic switches are widely used. For example, Auman and Dongfeng Tianlong have similar control principles.


In addition, the 13 Jiefang J6 is also equipped with a mechanical main power switch next to the battery, which is similar to the Jinbei light truck. The switch is installed in series on the negative main grounding wire of the battery. If this switch is disconnected, the circuit of the whole vehicle will be open.

Both Forms Of Dongfeng Tianlong Control The Positive Pole

For some models of Dongfeng Tianlong, the vehicle is separately equipped with electromagnetic power switch or mechanical power switch. Both switches are controlled + battery circuits.

Turning Off The Ignition Switch Is Unreliable And May Damage The Ecu

It should be pointed out that when the vehicle is carrying out welding and other operations, if the ignition switch is turned off alone, it is bound to damage the electronic control components on the vehicle, such as ECU, etc. The forum has had similar cases before.

Correct operation: first stop the engine and disconnect the main power switch. Disconnect the positive power line and negative power line of the battery (Note: negative before positive), and reliably connect the positive power line and negative power line before welding.

Other Matters Needing Attention: Loss Of Stored Information Due To Power Failure

With the continuous development of automotive technology, many electronic devices with storage and memory function are more and more widely used in vehicles. If the battery of the vehicle is powered off directly, it may lead to the loss of ECU stored fault information, locking of audio anti-theft password, reset of clock information and other problems, and then bring trouble to the use and maintenance of the vehicle.

The Characteristics Of Foreign Truck Technology Do Not Set The Main Power Switch

Forum card friends truck those things have been in their posts (click here) mentioned that the Mercedes Benz truck does not have a main power switch, because the on-board dash cam cannot be powered off according to the legal requirements. If the power is cut off and the battery runs out, the dash cam will not work, and it may bear legal responsibility. However, in order to ensure the reliable and normal operation of the power supply system, the Mercedes Benz truck adopts the following new design, the power supply is divided into two parts Equipped with system, battery instrument monitoring system and ultra-high fuse.


This article only briefly introduces the battery power-off operation and the form of power switch. Although there are various forms of power switch on the truck, it is recommended to power off the battery according to the maintenance operation procedures, especially when welding the body, so as to avoid damage to the vehicle electrical equipment. You are also welcome to discuss this issue.

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