Please keep in mind the wiring rules of automotive circuits

1. The characteristics and general rules of automobile wiring

Generally, a single-wire system is used, with electrical equipment connected in parallel, and the negative electrode grounded. The lines are distinguished by different numbers and colors, and are divided into several main lines with the ignition switch as the center.

1. Battery positive wire: lead through the fuse box from the battery, and some lead directly from the battery positive wire to the positive terminal of the starter, and then draw the thinner positive wire from there to other circuits.

2. Ignition, instrument, indicator line: the circuit can only be connected through the car key.

3. Dedicated line: electrical appliances that need to be connected regardless of whether the engine is working or not, such as a retractor and a cigarette lighter, are powered by a separate ignition switch.

4. Start control line: The control switch (contact plate) of the main circuit of the starter is usually turned on and off by a magnetic switch. It has three wiring methods: the attraction coil and the holding coil of the magnetic switch of the low-power starter are controlled by the start gear of the ignition switch; the attraction and holding coil of the high-power starter is controlled by the starter relay (such as Dongfeng Jiefang and Mitsubishi heavy vehicles); For cars equipped with automatic transmissions, in order to ensure neutral start, the start control line is often connected to the neutral switch in series.

5. Grounding wire: Grounding points are distributed throughout the car and connect with different metals (such as iron, copper and aluminum, aluminum and iron) to form an electrode potential difference. Some grounding parts are easy to be contaminated with muddy water, oil, or rust, and some grounding parts are very thin sheet metal, which may cause poor grounding, such as the instrument does not work, the horn does not sound, etc. Therefore, some cars use double wire.

2. Power system wiring rules

1. The generator is connected in parallel with the battery, and the negative electrode of the battery must be grounded. The positive pole of the battery is connected to the positive pole of the generator via an ammeter (or directly). The static electromotive force of the battery is usually 11.5V～13.5V, and the output voltage of the generator is usually limited to 13.8V～15V (24V electric system 28V～30V). The normal voltage of the generator is 0.3～3.5V higher than the voltage of the battery when it is working. This is mainly to overcome the line voltage drop, so that the battery can be fully charged and not overcharged.

2. There are marks or names on the terminals of the silicon rectifier generators made in China. "十" or "B 十" is the "armature" terminal. This terminal should be connected to the ammeter or the "十" pole of the battery; "F "Is the "magnetic field" terminal, which is connected to the "magnetic field" terminal of the regulator; "E" is the "ground" terminal, which should be connected to the "ground" terminal of the regulator.

3. There are two ways to ground the magnetic field coil of the AC generator with external regulator: one is that the magnetic field coil is ground directly inside the generator, such as the generator of the domestic Dongfeng EQ1092 BJ2020 automobile; the other is that the magnetic field coil is grounded through a regulator, such as the alternator of the Jiefang CA1092 car.

3. Wiring rules for starting the system

1. The ignition switch directly controls the circuit of the starter: the ignition switch directly controls the holding coil of the starter in the starting gear, which is mostly used in the car circuit of the starter of ≤1.2KW; the current of the magnetic switch coil of the starter of 1.5KW or more is above 40A and use the start relay contact as a switch.

2. Starter control circuit with starting protection: When the starting ignition switch is at gear 0, the circuits are all disconnected. When the ignition switch is in gear 1 (not started), the power supply circuit is provided by: generator excitation, ignition coil, instrument, and indicator light. When the ignition switch is in the 2nd gear, in addition to connecting the above circuit, it is also necessary to connect the starter relay circuit: the negative pole of the battery-ammeter-ignition switch-starter relay coil-relay normally closed contact-ground- the negative pole of the battery-the starter drive host.

At the same time, the contact bridge connects the bypass contact of the ignition coil, and the additional resistance is excluded. After the engine is ignited, the voltage to the ground at the neutral point N of the generator disconnects the start protection normally closed contact in the start relay, cuts off the grounding circuit of the charging indicator light, and the charging indicator light goes out, indicating that the generator is working normally.

At the same time, the grounding circuit of the starter relay coil is cut off. When the generator is working normally, even if the ignition switch is turned to gear 2 by mistake, the starter will not mesh with the flywheel, avoiding damage to the flywheel ring gear and the starter.

4. Ignition system wiring rules

Automobile ignition system can be divided into ordinary (contact) ignition system, non-contact ignition system, microcomputer controlled ignition system, etc. The working process is basically cycled in the following order: primary current is turned on-primary current is cut off- the primary coil generates self-induced electromotive force (about 300V)-the mutual inductance of the secondary coil generates pulsed high voltage (about 6000 to 30000V)-sparks appear in the spark plug.

The lead wires that the ignition module of the non-contact ignition system must have: 2 power input wires (4, 5 pins) controlled by the ignition switch, and the signal input wire from the signal generator (the signal generator and the distributor shaft are integrated) 3 lines (5, 5, and 3 pins, of which 5 pins are for the power supply line of the signal generator), and 2 primary current input and output lines (1, 2 pins).

5. Wiring rules of lighting system

Automotive lighting systems generally consist of headlights, width indicators (position lights), taillights (rear indicator lights), license plate lights, instrument lights, indoor lights, etc. The headlights are divided into high beams and low beams. , Controlled with a dimmer switch. The lighting is controlled by the light switch: the light switch is turned off at level 0, the small light is on at level 1 (including indicator lights, tail lights, instrument lights, and license plate lights), and the headlights at level 2 are on at the same time.

The current of the lighting system generally comes from the positive electrode of the battery and is not controlled by the ignition switch (because the high beam power of the headlight is relatively large, it is usually controlled by a light relay). The overtaking light signal is usually indicated by the high-beam light being on or off. This signal is not sent through the light switch and belongs to the short-term on-button type. The lighting system of modern cars is usually controlled by a combination switch. The combination switch is mostly installed on the steering column and located on the lower side of the steering wheel.

6. Wiring rules of instrument alarm system

1. All electrical instruments are controlled by the ignition switch.

2. The meter head of each instrument is connected in series with its sensor, and the fuel meter and water temperature meter are generally connected with an instrument voltage stabilizer.

3. The ammeter is connected in series between the positive pole of the generator and the positive pole of the battery. (The following two types of current do not pass through the ammeter: load current that exceeds the range of the ammeter, such as starters, glow plugs, horns, etc.; the current supplied to other loads when the generator is working normally.)

Note: When the generator is not working, the current supplied by the battery to other loads must pass through the ammeter.

4. The voltmeter is connected after the ignition switch, and only displays the system voltage when the ignition switch is turned on. 12V systems often use 10V~18V, 24V systems often use 20~36V voltmeters.

5. Indicator lights and warning lights are often assembled with the instrument in an assembly or arranged nearby. Together with the instrument, they are controlled by the working gear (ON) and starting gear (ST) of the ignition switch. In the ON position, it should be possible to check whether most of the meters, indicator lights, and warning lights are in good condition.

The indicator light and the warning light can be divided into two types according to the circuit connection: one is the light bulb is connected to the ignition switch live wire, and the sensor switch is connected externally. Such as: charging indicator light, hand brake indicator light, brake fluid level warning light, door open warning light, oil pressure warning light, low water level warning light, etc. Another connection method is that the indicator light is grounded, and the control signal comes from the live terminal of other switches. Such as: high beam indicator light, turn indicator light, seat belt not fastened indicator light, anti-lock brake indicator light (ABS), cruise control indicator light, etc.

6. The bimetallic heating wire structure is commonly used in automobile instruments, and the meter head generally has only 2 wires. For example, the two terminals of the fuel indicator are arranged up and down. Generally, the upper terminal should be connected to the power cord, and the lower terminal should be connected to the sensor, otherwise it will not work normally.

Mechanical instruments are not connected to the circuit, such as the speedometer of the flexible shaft drive, the direct-acting elbow spring brake pressure gauge, the oil pressure gauge, the ether expansion type water temperature gauge, the oil temperature gauge, etc. These instruments have high reading accuracy, but many pipelines and flexible shafts are introduced into the instrument panel, which is troublesome for disassembly and assembly, and even easy to leak. They are gradually being replaced by electronic control instruments.

7. Signal system wiring rules

The signal system mainly includes turn signal, hazard warning signal, brake signal, reversing signal, horn, etc. These signals are sent by the driver to other vehicles and pedestrians according to the road traffic conditions, with strong randomness, generally It is controlled by its own switch. For example, the brake signal is mostly controlled by the brake pedal linkage. The reversing lights are mostly controlled by the linkage of the shift lever reverse shaft, which can be turned on without the driver's special operation. The horn button is mostly on the steering wheel, and the driver can send a signal without leaving the steering wheel.

1. The turn signal lamp has a certain flashing frequency. The national standard stipulates that it is 60 ~ 120 magnets/min. The Japanese stipulation is (85 + 10) times/min. The power of the turn signal is often 21 ~ 25W, both front and rear, left and right. Large vehicles and cars often There is also a turn signal light on the side. The general connection method of the circuit is: turn signal and turn signal switch, turn flashing relay, connect in series with the ignition switch via the normally closed contact of the hazard warning light switch, that is, the turn signal light is used when the ignition switch is in the working position (ON).

Therefore, the hazard warning light can be used when the engine is not working, and there is no need to switch on the ignition system and the instrument warning light at this time. For this reason, a hazard warning switch is provided. While disconnecting the ignition switch wiring, turn on the battery wiring, the flasher and bulb power directly come from the battery, and connect the output terminals of the flash relay with the left and right turn signals. That is, when the flashing relay is activated, the left and right turn signals and the indicator lights simultaneously send out a hazard signal.

8. Wiring rules of electronic control system

The wiring rules of the electronic control system circuit can be summarized as: the computer control circuit must be controlled by the ignition switch, and there must be various sensors to input working condition signals at any time, for example: magnetic pulse type or Hall type sensors can generate pulse voltage signals. Some sensors are made of thermistors, the resistance changes, and the output voltage also changes accordingly. They are analog voltage signals, such as water temperature, intake air temperature sensors, etc.: The electronic control system actuator is controlled by a computer and has self-diagnosis function.

Computer work generally consists of two modes-open loop and closed loop control. For example, the open-loop control of fuel injection: After the engine computer receives the input signal, it only responds according to the preset program. Open loop operating conditions include warm-up operating conditions, deceleration operating conditions, and full throttle operating conditions. Closed-loop control: The engine computer detects the oxygen sensor signal, so that the computer-controlled fuel injection pulse width can obtain the ideal air-fuel ratio to achieve the best fuel economy and low emissions. The closed-loop operating conditions include idling operating conditions, cruise operating conditions, and so on.

9. Wiring precautions

1. Prepare the circuit schematic diagram of the vehicle to be wired. If there is no circuit diagram, it is best to draw a wiring sketch by yourself against the actual product, which will bring great convenience to the wiring maintenance work.

2. Due to the need for temporary external wiring for maintenance, attention must be paid to insulation to prevent short circuits.

3. Do not connect with live wires. When the wires are damaged, replace them with the wires of the original rules. Be careful when connecting, and minimize the contact resistance at the connections.

4. After the wiring is completed, it should be bound and handled according to the original wiring requirements.