07 Electric Sysetem LG958L

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LG958L Training Material

RELIABILITY IN ACTION1

Tuesday, May 19, 2015

Chapter X Electric System


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Structure, Characteristics, and Circuit Diagram Analysis of Electric System

CONTENTS

Power Supply and Starter System

Instrumentation and monitoring system

Automatic leveling of bucket

Lighting


Backup warning system

Wiper and washer

Electric horn

Spare socket


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Section I Composition, Structural Characteristics, and CircuitDiagram Analysis of Electric System of Loader

The electric system is an important

part of the loader and is mainly

functioned for start and control of

diesel engine and fulfillment of the

operations including lighting,


signal indicators, and instrumentmonitoring. The quality of electric

system directly influences the

working reliability and the traveling

and operation safety of the loader.


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The electric system of loader is mainly composed of the following 5 parts:

1. Power part: Including the battery and alternator assembly.

2. Start part: Mainly including starter, starter relay, and electric lock, whichare functioned to start the diesel engine.

3. Lighting and signaling part: Mainly including all kinds of lighting andsignal lamps and horns and buzzers, which are functioned to ensure thesafety of human and machine and the successful implementation ofo erations under all kinds of o eration conditions.

I. Main Composition of LG958L Electric System


4. Instrument monitoring part: Including pressure gauges, pressuresensors, temperature gauges, temperature sensors, and low pressurealarms.

5. Control part: Engine control unit and transmission control unit (detailed

in the engine system and transmission system).6. Accessory part: Including the electric wiper, heater, and A/C system.


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1. Low voltage:The rated voltage for electric system of the LG958L loader is 24V powered by two12 batteries in series connection.

2. DC

The diesel engine is started by the starter motor. The starter motor is a DC seriesexcitation motor that must be powered by battery. Therefore, the DC current mustbe used to charge the battery, which determines that the electric system of theloader is a DC system.

3. Sin le-wire s stem

II. Characteristics of Electric System of LG958L Loader


All electric devices are in series connection, namely only one wire is connectedfrom the positive post of power supply to the switch and the electric devices andthe metal bodies such as the loader frame, diesel engine block, transmission, andtorque converter are functioned as the public grounding wire. When thesingle-wire system is adopted, the wire that connected to the metal body is

referred to as grounding wire. The connection between the negative post ofbattery and metal body (such as frame) is referred to as negative groundingand the connection between positive post and metal body is referred to aspositive grounding.


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Expressing method of loader circuit diagram: The circuit diagram is a integralbody in which the power supply, starter system, lighting, instruments, andaccessories are connected by switches, wires, and fuses as per thecorresponding working characteristics and mutual internal relationship.

1) Expressing method for circuit diagram of loaderThe expressing methods include circuit diagram, schematic diagram,harness diagram, and distribution diagram of electric units.

2) Circuit analysis

III. Circuit Diagram and Malfunction Analysis Method ofConstruction Machinery


ng pr nc p es o c rcu s:

1. Single-wire system

2. All electric devices are in parallel connection and are controlled bycorresponding switches.

3. Low voltage. All electric devices adopt 24V design (the output voltage

of alternator is 28V).4. Negative grounding of battery.


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Every complete circuit is composed of power supply, fuse, switch, control device,electric device, and wires. The flow direction of the current must start from thepositive post of power supply, reach the electric device through fuse, switch,control device, and wires, and then return to negative post of power supplythrough wire (or grounding wire) to form the circuit. Therefore, there are threethoughts for reading the electric circuits:

Thought 1: Along the flow direction of the circuit current, start from the positivepost of the power supply, check the electric device, switch, and control device,and return to negative post of power supply.

Thought 2:Against the flow direction of circuit diagram, start from negative post

IV. Circuit Principles to be Borne in Mind


o power supp y eart ng an return to pos t ve post o power supp y t rougelectric device, switch, and control device.

Thought 3:Start from electric device, check the control switch, wires, and controlunit, and finally reach the positive post of power supply and grounding wire (ornegative post of power supply).

During the actual application, choose different thoughts depending on specificcircuit. However, please pay attention to this point that, following the extensiveapplication of the electric control technology, most of the electric device circuitsincorporate the main circuit and control circuit. Therefore, both circuits shall betaken into consideration while reading the diagram.


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Circuit diagram of LG958 electric system



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Section II Power Supply and Starter System



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Power circuits of engine and transmission



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The overall machine adopts 2 batteries inseries connection. The battery is oneinvertible DC power supply and is parallelconnected with alternator to power theelectric devices. A single battery can supply200A~600A start current to the starter motorwithin a short period (5~10s). The battery isalso equivalent to a large capacitor, whichcan absorb the over-voltage that may occurany time in the circuit, in order to protect the

I. Battery (6-QW-120B)


e ec r c ev ces aga ns punc ure.

Caution: The battery must be securely and reliably installed, in order toprevent damage due to bumps during traveling of the machine. Please turnoff the power switch when the machine is to be parked for a long time.

Warning: Please keep open fire away from the battery. Before the weldingoperations, please disconnect all connecting wires of the battery, in order toprevent explosion.


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ID rId2

1. Installation location of battery



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1 Green 2 Black 3 Light yellow 4 Battery cap 5 Observation

2. Structure and color change of charge indicator


window 6 Optic charge indicator 7 Green small ball

Figure 10-1 Structure and color of charge indicator

Color of chargeindicator

Electric quantity

The electric quantity is above 65% and thebattery is normal

The electric quantity is less than 65% and thecharging is required.

The battery is over-charged and shall bereplaced with new one.


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The electric quantity of the battery can be understood via the color change ofcharge indicator (also referred to as charge indication densimeter). Green Normal, black to be charged, light-up (or white) depleted.

When the machine cant be started, firstly please check the electric quantity of

the battery and check the battery cables for reliable connections.Caution: While frequently checking the battery cable connections andconnecting points for reliable connections, please firstly disconnect thenegative post of power supply.

2. Structure and color change of charge indicator


At the time of assembly, firstly assemble the positive post of battery and thenassemble the negative post. At the time of disassembly, firstly disassemble thenegative post and then disassemble the positive post. This is intended toprevent the short-circuit from damaging the battery posts and wrenches.

Check method for terminal voltage of battery: Check with DC 200V measuring

range of multimeter. Connect the red probe to the output cable end of thepositive post of battery and connect the black probe to the negative post of thebattery. The reading of the multimeter is the terminal voltage of the battery(generally at 24V~26V).


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Power switch (K01K18-A, also referred to asnegative switch):

The power switch controls the connection anddisconnection between battery negative postand frame (grounding). Turn on the powerswitch to connect the negative post of batterywith frame. Turn on the electric lock to poweron the electric loads of overall machine. Turn offthe power switch to cut off the negative post ofbattery from frame so that no loop is formed inthe circuits of the overall machine. Even whenthe electric lock is turned on, the overallmachine cant be owered on nor started. The

II. Power switch


installation location of the power switch isshown in Figure 10-2.

Operations of power switch: is turn-offposition and is turn-on position.

Warning: When the loader is parked for a long time, please ensure to

turn off the power switch, in order to prevent electric leakage andother accidents. Before connecting the battery cables, re-tighteningthe battery cables, or disconnecting the connecting wires of battery,please make sure to turn off this switch for the purpose of safety.

Figure 10-2 Power switch


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2. The unidirectional conduction performance of silicone diode isutilized for rectification. At any moment, only the positive diodeconnected with the winding of the phase with highest potential is on.In same way, the negative diode connected with the winding of thephase with lowest potential is on. Through the sequential turn-on ofsix diodes repeatedly, one relatively stable pulsed DC voltage isobtained at two sides of the load.


3. The terminal voltage of alternator is proportional to the speed of thealternator. Due to high speed variation range of the engine, theterminal voltage of alternator will also vary within a high range andthe output of terminal voltage can't meet the operation requirementsof the loaders electric devices for constant voltage. Therefore, the

voltage regulator must be set.


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Figure 10-3 Schematic diagram of alternator

4. The voltage regulator utilizes the on/off of switching tube to change the size ofexcitation current so as to change the intensity of magnetic field to stabilize thevoltage of the alternator.

5. The filter capacitor is mainly functioned to filter away the peak pulse and highfrequency interference issued by the alternator.


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The alternator is generally an assorted part of

diesel engine and has three lead terminals, asshown in the Figure 10-4, which arerespectively:B+: Alternator power output terminalD+: Charging indicator signal

W+: Phase output terminal, which can befunctioned as timer signal as well asspeedometer signal.The alternator is in parallel connection withbattery set to power the electric devices of

3.2 Wiring method of alternator


whole loader. The electric devices arepowered by the battery before the start of theloader and are powered by the alternatorafter the start of loader. At the same time, thealternator also charges the battery set.

Figure 10-4 Alternator

Warning: Its strictly prohibited for the alternator to independently power theelectric devices without the battery.

Warning: Its prohibited to check the power generation of alternator by instantlyshort-circuiting the positive and negative posts of alternator for generation ofspark, in order to prevent burning the diode and impairing the regulator.


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1. Check with DC 200V measuring range of multimeter. Turn on the electriclock, measure the terminal voltage of alternator (connect red probe toterminal D+ of alternator and connect black probe to grounding), andrecord the reading of multimeter (This reading is actually the terminal

voltage of battery and is generally less than 26V). Start the machine,measure the terminal voltage of alternator again, and record thereading of multimeter (If the alternator is generating power normally,this reading shall be approximate 28V).

3.3 Judgment method for normal power generationof alternator and treatment


2. Treatment

If the alternator fails to generate power or the voltage generated is toolow, firstly check the drive belt of alternator for looseness. Turn off the

electric lock and use wrench to check the wiring terminals of alternator forcorrect, tightened, and reliable connections. In addition, check thealternator for reliable grounding.


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IV. Starter system



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IV. Composition of starter system



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I. Structure of starter motor

The starter motor is an assortedunit of diesel engine. It is mainlycomposed of electromagneticswitch, DC motor, shifting fork,and drive gear. The starter motor

converts the electric energy ofthe battery to mechanical energythrough DC motor and drives theengine flywheel through drive


Warning: After the engine is started, immediately release the starter switch, or itwill lead to damage of drive gears, burnout of DC motor, damage of flameoutelectromagnet, and serious impairment of service life of the battery.

Caution: Please frequently check the wirings of contacts and terminals forreliable connections. Before the checking, make sure to disconnect the negativepost of power supply, or it will probably generate short-circuit spark and damagethe wrench and wiring posts.

Figure 10-5 Exterior view of starter motor

gear to realize the start ofengine.


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2. Internal structure of starter motor

RELIABILITY IN ACTION25Figure 10-6 Internal structure and principle description of starter motor


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When the power switch is turned on, the 24V terminal voltage of the battery is applied

onto the starter motor via the contact of starter relay. At the moment when theelectric lock is rotated to position START, two coils of the electromagnetic switchof the starter motor are powered and actuated. The electromagnetic resultant forcegenerated by above two coils drives the movement of movable contact disc so thattwo contacts of the electromagnetic switch are engaged and the current is inputted to

the DC motor coil from the battery for form the circuit via the housing of startermotor. In such case, the DC motor starts the rotation. At the same time, the iron coremoves to drive the shifting fork to engage the drive gear with the engine flywheelgear ring. The DC motor drives the rotation of the flywheel and the engine start isinitiated.

3. Working principle of starter motor



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During the start process (within more than 10s when the electric lock is rotated to

position START), the 1# wire is constantly live (24V) and the contacts 1# and 2# are

constantly engaged. As the contact voltage is 24V, the voltage is equal between two

terminals of the pull-in coil and no current is flowing. In such case, the iron core is

maintained at start status under the action of the electromagnetic force of the holding

coil. When the driver release the electric lock key after the successful start of the

engine, the electric lock automatically returns to position ON and the 1# wire is

powered off immediately. Within a really short period, the flow direction of the current


is contact 1# - contact 2# - pull-in coil terminal S holding coil, and grounding. It canbe seen that the current flow direction is opposite between the holding coil and pull-in

coil. As the magnetic fields generated are in opposite directions, the electromagnetic

forces applied onto the iron core are cancelled out with each other and the iron core

returns to initial position under the action of spring force. In such case, the contacts 1#

and 2# are disengaged, no current flows through the pull-in coil and holding coil, and

the driver gear resets to initial position. The starter motor stops working.


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1) Malfunction symptom: The starter motor runs automatically after thenegative switch is turned on.

Cause analysis: This symptom is generally caused by the ablated contacts of

starter relay, electric lock, or electromagnetic switch.

Treatment: Re-grind the contacts and movable contact disc or replaceelectromagnetic switch or starter motor.

4. Judgment for common malfunctions of starter motor:


2) Malfunction symptom: No reaction of starter motor at the time of start.

Treatment: While rotating the electric lock to position START, check thewire voltage at the electromagnetic switch of pneumatic motor. If novoltage is detected, check the electric lock, starter relay, and battery (For

instance, check the battery set connecting circuit, negative switch, andgrounding wire for reliable connections), or it can be determined as themalfunction of starter motor that leads to start failure.


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Starter switch



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Batter rela


B a c k


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Transmission control unit (ECU)


Engine control unit (ECU)

B a c k


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Electric pump


B a c k

S ti III I t t ti d it i t


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Section III Instrumentation and monitoring system1. Circuit diagram of instrumentation systemThe instrumentation system includes the instrument panel assembly, sensor, and alarmpressure switch, of which the schematic diagram is shown in Figure 3-1.

T r a n s m i s s i o n o i l

p r e s s u r e g a u g e

I n s t r u m e n t p a n e l

L o w p r e s s u r e

a l a r m

E n g i n e w a t e r

t e m p e r a t u r e

g a u g e

T o r q u e

c o n v e r t e r o i l

t e m p e r a t u r e

g a u g e

V e h i c l e s p e e d

g a u g e

B r a k i n g a i r

p r e s s u r e g a u g e

W o r k i n g

h o u r m e t e r

F u e l g a u g e

H i g h b e a m

i n d i c a t o r

L e f t t u r n

l a m p

L o w e n g i n e o i l

p r e s s u r e

w a r n i n g l a m p

E m e r g e n c y

t u r n l a m p

S t r a i n e r


P r e h e a t i n g

i n d i c a t o r

H a n d b r a k e

i n d i c a t o r

C h a r g i n g

i n d i c a t o r

L o w a i r

p r e s s u r e


P o w e r

c u t o f f l a m p

P o w e r c a s e

w o r k i n g l a m p

R i g h t t u r n l a m p


Figure 10-7: Schematic diagram of instrumentation and alarm system

E m e r g e n c y t u r n

a l a r m

F l a s h e r

E n g i n e w a t e r

t e m p e r a t u r e s e n s o r

B r a k i n g p r e s s u r e

s e n s o r

P a r k i n g b r a k e i n d i c a t o r

s w i t c h

E n g i n e o i l

p r e s s u r e s w i t c h

F u e l l e v e l s e n s o r

T o r q u e c o n v e r t e r o i l

t e m p e r a t u r e s e n s o r

S t r a i n e r

w a r n i n g s w i t c h


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2. Sensors


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2.1 Temperature Sensor

LG958L is fitted with two temperature sensors to monitor the torque converter oiltemperature and engine water temperature. The temperature sensor is equivalent toa thermistor, of which the resistance is reduced along with the increasing oftemperature. (226Ohm at 26C ambient temperature and 26.4Ohm at 115C)


Figure 10-10 Torque converter oiltemperature sensor

Figure 10-9 Exterior view oftemperature sensor

2 2 Braking air pressure sensor


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2.2 Braking air pressure sensor


The swing of the instrument pointer is achieved by the change of current arisingfrom the slide of resistor pointer within the sensor, which is caused by thedeformation of beryllium bronze diaphragm due to change of pressure, as shown in

Figure 10-11.2.3 Fuel level sensor

The fuel level sensor is actually a discrete slide resistor, of which the resistance isreduced along with the increasing of fuel level. Its installed on the fuel tank.

Figure 10-11 Internal structure of braking air pressure sensor

2.5 Alarm pressure switch


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pThe overall machine is fitted with two pressure switches, namely low brakingpressure alarm switch and low engine oil pressure alarm switch.

The specific installation positions are shown in Figure 10-13 and Figure 10-14respectively.The alarm indicator will alarm when the braking air pressure is less than0.45MPa or the engine oil pressure is less than 0.08MPa.


Figure 10-13 Low braking pressurealarm switch

Figure 10-14 Engine oil pressure alarmswitch

3 Examples for troubleshooting of common malfunctions of


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3.1 Abnormal indication of temperature gauge

Disassemble the sensing wire from the temperature sensor (the torque converteroil temperature gauge and the water temperature gauge correspond to wire 15#and wire 14# respectively). If the instrument indicates full measuring range when

the sensing wire is grounded and indicates minimum reading when the sensingwire is hung in the air, it indicates that the instrument and circuit are normal andthe sensor is damaged. Replace the sensor. Otherwise, check the circuit. If thecircuit is normal, the instrument is malfunctioned.

3. Examples for troubleshooting of common malfunctions ofinstrumentation and monitoring system


3.2 Abnormal fuel level indication

Disassemble the sensing wire (wire 19#) from the fuel level sensor. If theinstrument indicates full measuring range when the sensing wire is grounded andindicates minimum reading when the sensing wire is hung in the air, it indicates

that the instrument and circuit are normal and the sensor is damaged. Replace thesensor. Otherwise, check the circuit. If the circuit is normal, the instrument ismalfunctioned.

Section IV Automatic Resetting System of Bucket


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1. Schematic diagramThe schematic diagram is shown in Figure 10-15.

Section IV Automatic Resetting System of Bucket

P r o x i m i t y s w i t c h ( b o o m )

L o a d

B r o w n B l u e

B r o w n

F l o a t i n g

s o l e n o i d v a l v e

B u c k e t s o l e n o i d

v a l v e

B o o m s o l e n o i d

v a l v e


Figure 10-15: Schematic diagram for circuit of automatic resetting system

P r o x i m i t y s w i t c h ( b u c k e t )

Normally closed (N.C.)

B l a c k

B l u e

B l u e

B r o w n

B r o w n

B l a c k

B l a c k

1 1 Bucket leveling limiter:


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1.1 Bucket leveling limiter:

This device is composed of proximity switchinstalled on the bucket cylinder bracket (as shownin Figure 10-16) and solenoid valve on the pilotvalve. There is a red indicator on the proximityswitch, which indicates the status of the proximityswitch. When the retraction rod is misplaced fromthe proximity switch, the proximity switch is turnedoff, the red indicator goes off, and there is no

output signal in the black output wire. If the driverpulls the bucket operating lever to the mostrearward position when there is no unloading anglefor the bucket, the magnetic circuit is turned on sothat the electroma netic field force enerated b


the solenoid coil will hold the bucket operating

lever (in such case, the driver may release theoperating lever and the bucket operating lever willnot return to neutral position) and the bucket willkeep retracting, till the proximity switch approachesthe retraction rod. In such case, the proximityswitch is turned on, the red indicator lights up, the

solenoid coil is turned off, and the magnetic forcedisappears so that the bucket operating leverautomatically returns to neutral position under theaction of spring force and the bucket stops atleveling position.

Figure 10-16 Bucket retractionrod and proximity switch


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1.2 Boom floating device

This device does not incorporate the proximity switch and onlyincorporates a boom floating coil that is located on the pilot valve. Afterthe electric lock is turned on, the coil is powered on constantly. When thedriver pushes the operating lever to most forward position, the magnetic

circuit is turned on so that the electromagnetic field force generated by thesolenoid coil will hold the boom operating lever (in such case, the drivermay release the operating lever and the boom operating lever will notreturn to neutral position) and the pilot valve connects the oil lines of


ro ess an ro c am ers o oom cy n er w e o p pes y

controlling the distributor valve. In such case, the pressure is zero for bothrodless and rod chambers and the pressure difference is also zero. If thedriver pushes the boom operating lever to floating position during theloading operations, the bucket will fluctuate along with the ups and downsof the ground. If the driver pushes the boom operating lever to floating

position to operate the lowering of boom, the boom will lower at fastestspeed under the action of dead weight, in order to improve the workingefficiency.


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1.3 Troubleshooting of system malfunctions

Check 10A fuse for burnout.

Check all connectors for good connections.

Check gap between metal body and proximity switch (generally nomore than 8~10mm).

Check proximity switch for damage: Turn on the electric lock. The redindicator shall light up when the metal body approaches (Whenmeasured with multimeter, the black output wire shall be connected to


ground).

Check the pilot coil: The resistance is approximate 100~200Ohm forthree pilot coils.

Section V Lighting System


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Section V Lighting System


1. Circuit of front combination lamp


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p1.1 Schematic diagram for circuit of front combination lamp

R i g h t c o m b i n a t i o n l a m p

L e f t r e a r l a m p

R i g h t r e a r l a m p

W a r n i n g l a m p s w i t c h

C o m b i n a t i o n s w i t c h

( h e a d l a m p

l o w b e a m )

( h e a d l a m p

h i g h b e a m )

L e f t c o m b i n a t i o n l a m p

G r e e n B r o w n Y e l l o w R e d B l a c k G r e y B l u e

O r a n g e

W h i t e

T e r m i n a l

P o s i t i o n

O f f

L e f t

t u r n

R i g h t

t u r n

B a c k l i g h t

H

e

a

d

l

a

m

p

H i g h

b e a m

L o w

b e a m

O v e r t a k i n g

l a m p

G

r

e

e

n

B

r

o

w

n

Y

e

l

l

o

w

R

e

d

B

l

a

c

k

G

r

e

y

B

l

u

e

O

r

a

n

g

e

W

h

i

t

e

T e r m i n a l

P o s i t i o n

O f f


Figure 10-18: Schematic diagram for circuit of front combinationlamp, turn lamp, and warning lamp

R i g h t c o m b i n a t i o n l a m p

L e f t c o m b i n a t i o n l a m p

R

e

s

e

r

v

e

d

1 2 P i i l d i ti


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1.2 Principle description

When the electric lock is turned on, the 10A headlamp fuse withinthe 20-circuit fuse case is turned on (24V) to turn on thecombination switch via wire 44# and turn on the contact of high

beam/low beam relay of front combination lamp via wire 35#. Whenthe combination switch is not turned on, the wire 49# and wire 50#are not turned on and both left and right headlamps are notworkin . When the combination switch is at hi h beam or low beam


position, the wire 49# or 50# is turned on (24V) and the coil of highbeam/low beam relay of front combination lamp is turned on andactuated so that high beam or low beam of front combination lampis turned on (24V) and left and right headlamps work atcorresponding position.

1 3 T bl h ti f lf ti f t


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1.3 Troubleshooting of common malfunctions of system Lighting failure of headlamp

1.3.1 Check the bulbs for blackening. If yes, it can be determinedthat the bulbs are damaged. Replace the bulbs.

1.3.2 Unplug the connector, shift the dimmer switch to high beam

position and low beam position respectively, and measure thevoltage between wire 49# and wire 50# at the connector withDC voltage measuring range of multimeter. If the voltage is


, .

connection is loose, re-connect. If the connection is secure,the internal wire of headlamp is loose or the bulb is damaged.If the voltage is 0V, check as below.

1.3.3 Check the 10A headlamp fuse for burnout.1.3.4 Check the connectors for reliable connections and check the

harnesses for wear.1.3.5 Check the functions of dimmer switch positions as per the

Accessories Combination Switches.

2. Circuits of working lamp, rear lighting lamp, and


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interior lamp

Rocker switch of rear lighting lamp (high beam and low beam)

Rear lighting lampRear lighting lamp

OFF

T e r m i n a l

P o s i t i o n


Figure 10-19: Schematic diagram of rear lighting lamp

Rocker switch of headlamp Rocker switch of rear illuminator


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Rocker switch of headlamp

HeadlampHeadlamp

Rocker switch of rear illuminator

OFF OFF

T e r m i n a l

P o s i t i o n

T e r m i n a l

P o s i t i o n


Figure 10-20 Schematic diagram for headlamps and rear illuminators

2.1 Four lamps on the top front and rear of the cab are defined as headlamp and rear illuminator,two lamps on the rear hood are defined as rear lighting lamp. The switch of interior lamp is

attached. Refer to Accessories Rocker Switches for details of switches of rear lighting lampsand working lamps.

2.2 Schematic diagram: As shown in Figure 10-19 and Figure 10-20.2.3 The basic principle and the troubleshooting of system malfunction are basic same with the

headlamp circuit and are omitted herein.

3. Circuit of turn lamps:


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3.1 Schematic diagram: As shown in Figure 10-18.

3.2 Introduction of main units:3.2.1 The actual combination switch and installation position are shown in Figure 5-

4 and Figure 5-5 respectively. The turn lamp switch is realized by partialfunction of the combination lamp and the wire colors of three pins used aregrey, yellow, and white, of which the grey wire is connected to turn flasher

power supply (wire 33#), the yellow wire is connected to left turn signal wire(wire 6#), and the white wire is connected to right turn signal wire (wire 7#).


Figure 10-21 Combination switch Figure 10-22 Installation position of combination switch


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3.2.2 Flasher relay (SG252): Three pins of the flasher are defined as below:

B power terminal, connected to wire 21#; L Flasher signal outputterminal, connected to wire 33#; E Grounding, connected to wire0#. During normal working, the flasher relay will issue slightrattle sound at a frequency of approximate 50 cycles/min.Otherwise, it can be determined that the flasher relay is damaged.

3.2.3 Warning lamp switch: The parking lamp switch controls four turnlamps and two turn indicators on the instrument panel. When thisswitch is turned on, four turn lamps and two turn indicators flash atthe same time to alert the vehicles crossin b .


The basic principle and the troubleshooting of system malfunctionare basic same with the headlamp circuit and are omitted herein.

4. Circuit of clearance lamp:4 1 Schematic diagram: As shown in Figure 10 23


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4.1 Schematic diagram: As shown in Figure 10-23.

Right rear lamp

Right combination lamp

Left rear lamp

R o c k e r s w i t c h o f

b a c k l i g h t

T

e

r

m

i

n

a

l

P

o

s

i

t

i

o

n

O

F

F


Figure 10-23: Schematic diagram for circuit of clearance lamp

Left combination lamp


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Figure 10-24: Combination headlamp Left Figure 10-25: Left rear tail lamp


4.2 The installation positions of the clearance lamps are shown in Figure10-24 and Figure 10-25.

4.3 The basic principle and the troubleshooting of system malfunction are

basic same with the headlamp circuit and are omitted herein.


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5. Brake lamp circuit:5 1 Schematic diagram: As shown in Figure 10-26


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5.1 Schematic diagram: As shown in Figure 10 26.

To ECU case

Intermediate relay

(start interlock)Intermediate relay(power cutoff)

Intermediate relay

(backup)


Figure 10-26: Schematic diagram for circuit of brake lamp

To terminal G2 of starter

switch

Parking brake indicator switch

To backup lampTo starter relay signal

terminal

To instrument panel ECU case indicator

Brake switch (left)

To brake lamp

Brake switch (right)

5.2 Principle description:

When the brake pedal is depressed, the braking air pressure at the brake lamp switch engages the


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p p g p p g gcontact of brake lamp switch so that the current flows to brake lamp through 10A fuse, wire 57# at

brake lamp fuse, brake lamp switch, and wire 8# to light up the brake lamp.5.3 Brake lamp switch: The switch adopts normally open contact, which acts and engages at

approximate 1.3bar.

Troubleshooting How to judge the damage of brake lamp switch: Firstly determine whether thebraking pressure is normal (turn on the electric lock. If the low service braking pressure alarm lamp

on the instrument panel is off, it indicates that the braking pressure is normal. Otherwise, start theengine, till the low service braking pressure alarm lamp is off). If normal, unplug the wire at the brakelamp switch and measure two pins of the switch with 200Ohm measuring range of multimeter. If themeasurement differs from the table below, it indicates that the pressure switch is damaged and shallbe replaced.


Brake pedal is notdepressed

OFF

Brake pedal isdepressed

ON

Figure 10-27: Installation position of brake lamp switch

Section VI Backup Warning System


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Right rear lamp Left rear lamp Backup buzzer

Backup switch


1. Principle description:

When the electric lock is turned on, the 10A backup warning fuse is turned on (24V).When shifted to reverse gear, the backup switch is turned on, the wire 9# is turned on,and the backup warning buzzer sounds. At the same time, the backup lamps on the leftand right rear lamps light up.

Figure 10-28 Schematic diagram for backup warning system

2. Analysis of Common Malfunctions


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The backup warning buzzer fails to sound when the electric lock is turned on andthe reverse gear is engaged.

1. Check the 10A backup warning buzzer fuse for burnout.

2. Check the connectors and wires for secure and reliable connections. Generally,the loose connector or worn harness will lead to middle open-circuit of wire 9#.

3. Check the backup switch for damage. If normal, two wires of the backup switchare connected when the reverse gear is engaged.


. ,

at the backup warning buzzer. If the voltage is normal (24V), it indicates that thebackup warning buzzer is damaged and shall be replaced. If no voltage isdetected, generally the connector is loose or the harness is worn.

Analysis of common malfunctions: After the electric lock is turned on, the backupwarning buzzer sounds constantly no matter which gear is engaged. This problem

is generally caused by the bonded contact of backup switch. In few cases, itscaused by the short-circuit between wire 9# and certain power wire.

Section VII Wiper and Washer System

1 P i i l d i ti


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1. Principle description

1.1 Principle of washer: When the electric lock is turned on, the 10A wiper fuse is poweredon (24V) to turn on the washer switch (its an automatic resetting rocker switch. Pleaserefer to the Accessories Rocker Switch for details) so that the washer motor (installedon the water reservoir) is powered on via wire 37# to pump the water from waterreservoir to the nozzles (installed beneath the front windscreen of the cab) and sprayonto the windscreen.

R o c k e r s w i t c h o f w a s h e r r e s e r v o i r ( w i t h r e s e t t i n g

f u n c t i o n )

R o c k e r s w i t c h o f f r o n t w i p e r

O F FO F F

T e r m i n a l

P o s i t i o n

T e r m i n a l

P o s i t i o n


Figure 10-29 Schematic diagram of wiper and washer system

S p r a y m o t o r

F r o n t w i p e r

1.2 Principle of wiper:

The wiper motor is a permanent magnet motor that adopts the positive control


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The wiper motor is a permanent magnet motor that adopts the positive control

mode.As shown in the figure, the wiper motor has 4 output wires, of which the red isthe power wire (the public wire for high speed armature and low speedarmature), the black wire is the resetting wire, the blue wire is another brush wirefor high speed armature, and the white wire is another brush wire for low speed

armature. When the electric lock is turned on, the wire 37# is powered on (24V).If the wiper switch (refer to Accessories Rocker Switch for details) is at positionI, the pin 37# and pin 24# are connected and the motor runs under low speedmode.


If the wiper switch is at position II, the pin 37# and pin 26# are connected and

the motor runs under high speed mode.If the wiper switch is turned off (namely rotate from position I to positionOFF), the pin 24# and pin 25# are connected. At the wiper is not stopped atthe initial position at the moment when the switch is turned off, the current flowsthrough wire 25# - wiper switch pin 24# - low speed armature grounding

(Note: There is an internal automatic stop device to ensure that the wiper alwaysstops at initial position. When the wiper is at initial position, the resetting wire isconnected to the ground).

2. Troubleshooting of common malfunctions


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2.1 Working failure of wiper motor

1. Check 10A wiper fuse for burnout.

2. Check wiper switch for damage.3. Check connectors for looseness and harnesses for wear.

4. Check wiper motor armature for short-circuit or open-


circuit.

2.2 No water spray from nozzles

1. Observe the motor for running and pumping of water.

2. Check water line for interruption (The water pipe is

disconnected or over-tightly bundled).

3. Check the nozzles for blockage.

Section VIII Electric horn system


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Horn assembly

Horn button


1. Principle description:When the electric lock is turned on, the 10A electric horn fuse is turned on

(24V). When the electric horn switch is pressed, the current flows through10A electric horn fuse electric horn electric horn switch grounding andthe electric horn sounds continually (as shown in Figure 8-2).

Figure 10-30: Schematic diagram for circuit ofelectric horn

Figure 10-31: Installationlocation of electric horn



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The electric horn fails to sound when the electric lock is turned on and theelectric horn switch is pressed:

2.1 Check 10A electric horn fuse for burnout.

2.2 Check electric horn switch (the button switch in the center of steeringgear) for normal functioning. Normally, the wire 12# is groundedwhen the electric horn button switch is pressed.

2.3. Check connectors for looseness and harnesses for wear.


.

electric horn, connect one post to 24V power supply and connectanother to ground. If the electric horn fails to sound, it can bedetermined as the damage of electric horn).

Section IX Spare Socket System


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Spare socket


1. Principle description

When the electric lock is turned on, the 10A spare socket fuse is turned on (24V) to turn onthe spare socket through wire 77# and wire 0#. When the external power supply is required,

after the external wire and plug are correctly connected, insert into the socket to obtain thepower. Please be noted that the consuming power shall not exceed 150W. The spare socketprovides a standard DC 24V power socket for connection of external loads such as electrickettle and interphone. The installation position is shown in Figure 10-33.

Figure 10-32: Schematic diagram forcircuit of spare socket Figure 10-33: Installationposition of spare socket


ki f il f k


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Working failure of spare socket:

2.1 Check the 10A spare socket fuse for burnout.

2.2. Check connectors for looseness and harnesses for wear.

2.3 Check the spare socket for damage.


THE ENDTHE ENDTHE ENDTHE END


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07 Electric Sysetem LG958L

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