LEXUS SC400 1991 Service Repair Manual

Wiring Diagram
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BODY ELECTRICAL SYSTEM Power SourceBE±15
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Replacement of Relays
REPLACEMENT OF RELAY IN RELAY
BLOCK NO. 1, NO. 4 and NO. 5
1. REMOVE FOLLOWING PARTS:(See page BO±112)
(a) No. 1 under cover.
(b) Door scuff plate.
(c) Floor carpet.
2. REMOVAL AND INSTALLATION OF RELAY
(a) Remove the junction block No. 1 set bolts.
(b) Disconnect connectors.
(c) Separate the relay block No. 4 and No. 5 from the junction block No. 1.
(d) For installation follow the removal procedure in reverse.
Replacement of Relay Block No. 2
(A)
REPLACEMENT OF RELAY BLOCK NO. 2
(A) IN RELAY BLOCK NO. 2
1. REMOVE RELAY BLOCK NO. 2 (A)
(a) Remove the battery. CAUTION: Work must be started after approx. 20 se-
conds or longer from the time the ignition switch is
turned to the ºLOCKº position and negative (±) terminal
cable is disconnected from the battery.
(b) Remove the relay block No. 2 cover.
(c) Pry loose two locking lugs and remove the nut.
2. INSTALL RELAY BLOCK NO. 2 (A) For installation follow removal procedure in reverse.
BE±16
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BODY ELECTRICAL SYSTEM Power Source
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REPLACEMENT OF RELAY BLOCK NO. 2
(B) IN RELAY BLOCK NO. 2
1. REMOVE RELAY BLOCK NO. 2 (B)
(a) Disconnect the battery terminals.CAUTION: Work must be started after approx. 20 se-
conds or longer from the time the ignition switch is
turned to the ºLOCKº position and negative (±) terminal
cable is disconnected from the battery.
(b) Remove the relay block No. 2 cover.
(c) Remove the relay block No. 2 lower cover.
2. INSTALL RELAY BLOCK NO. 2 (B) For installation follow the removal procedure in reverse.
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BODY ELECTRICAL SYSTEM Power SourceBE±17
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Description
The power source supplies power to each of the vehicle's electrical devices. It is composed of the battery, fuses
and relays, which are located centrally at relay block No. 2 and relay block No. 6 i\
n the engine compartment
and junction block No. 1 relay block No. 4 and relay block No. 5 in the \
cabin near the driver's feet.
Related systems for each Fuse
No.Part NameRelated Systems or Parts
1IGN
Charging System
AIR±BAG System1IGN
Engine
2ST
Starter
3WIPER
Wiper and Washer System
4HTR
Defogger System
A/C System
5ENGINE
Charging System
6RADIO NO. 2
Audio System
Power Mirror System

Cigarette Lighter
A/C System
7CIG
Combination Meter System
AIR±BAG System7CIG
Shift Lock System
Theft Deterrent System

TEL System
8STOP
Stop Light System
Cruise Control System
9TURN
Turn Signal and Hazard
Warning Light System
Cornnering Light System
10MIR HTR
Mirror Heater System
11PANEL
Illumination Light System
12ECU±B
Combination Meter System
AIR±BAG System

Combination Meter System
ECT System
13GAUGE
Back±Up Light
Transmission Indicator

Light Failare Sensor
ABS and TRAC

Power Seat System
Door Lock Control System

TEL System
Shift Lock System
14ECU±IG
Radiator Fan
Auto Antenna

Electric Tension Reducer System
Power Steering

Auto±Tilt away Steering
Cruise Control System
15TAIL
Taillight System
Side Marker15TAIL
Clearance Light
16DOOR
Power Seat System
Luggage Door Opener16DOOR
Door Lock Control System
Fuel Lid Opener System
17IG SWUpstream of ECU±IG, ENGINE, WIP, HTR, TURN, GAUGE, and ST Fuse
18PWR
Power Window System
Sliding Roof System
19ABS NO. 1
ABS and TRAC
20AM1Upstream of MIR HTR, TAIL, PANEL, STOP, ECUA±B, DOOR and PWR Fuse
21ALTUpstream of DEF, HTR, AM1, and ABS No. 1 Fuse
BE±18±
BODY ELECTRICAL SYSTEM Power Source
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No.Part NameRelated Systems or Parts
22MAIN
Upstream of ALT±S and EFI Fuse
23AM2
Charging System
Engine23AM2
AIR±BAG System
24ABS NO. 2
ABS and TRAC
25INJ
Charging System
Engine25INJ
AIR±BAG System
26DEF
Defogger System

Power Seat System
Sliding Roof System

A/C System
Liquid Crystal Inner Mirror System
27DOME
Combination Meter System
Interior Light System27DOME
ABS and TRAC
Wireless Door Lock Control System

Cruise Control System
Auto±Tilt away Steering

Theft Deterrent System
28EFI
Engine
29HAZ HORN
Turn Signal and Hazard Warning Light System29HAZ±HORN
Horn System
30RADIO NO. 1
Audio System
31TEL
TEL System
32ALT±S
Charging System
33TRAC
ABS and TRAC
34HEAD (RH±LWR)
Headlight System
35HEAD (LH±LWR)
Headlight System
36HEAD (RH±UPR)
Headlight System
37HEAD (LH±UPR)
Headlight System
38HTR
Blow Motor
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BODY ELECTRICAL SYSTEM Power SourceBE±19
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Inspection of Power Source Circuit
INSPECTION OF JUNCTION BLOCK NO. 1
1. INSPECT FUSE CIRCUITRemove the fuse from the junction block and inspect the con-
nector on junction block side as shown.
FuseCheck forTester connectionConditionSpecified value
IGNVoltage1±GroundIgnition switch turned to ONBattery voltage
ST
g
4±GroundIgnition switch turned to START
yg
WIPER5±GroundIgnition switch turned to ON
HTR8±Ground
g
ENGINE9±Ground
RADIO NO. 211±GroundIgnition switch turned to ACC or ON
CIG14±Ground
g
STOP15±GroundConstant
TURN18±GroundIgnition switch turned to ON
MIR HTR20±GroundIgnition switch turned to ON and defogger
switch turned to ON
PANEL21±GroundLight control switch turned to TAIL or HEAD
and *Engine Running
ECU±B27±GroundConstant
GAUGE29±GroundIgnition switch turned to ON
ECU±IG32±Ground
g
TAIL33±GroundLight control switch turned to TAIL or HEAD
and *Engine Running
DOOR35±GroundConstant
IG SW38±Ground
POWER39±Ground
If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect the circuits connected to other parts.
BE±20
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BODY ELECTRICAL SYSTEM Power Source
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2. INSPECT RELAY CIRCUITRemove the relay from the junction block and inspect the
connector on junction block side as shown.
RelayCheck forTester connectionConditionSpecified value
TAILVoltage(1)±GroundConstantBattery voltage
(4)±Ground
P/W MAIN(6)±Ground
If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect the circuits connected to other parts.
INSPECTION OF RELAY BLOCK NO. 2
1. INSPECT FUSE CIRCUIT Remove the fuse from the relay block and inspect the con-
nector on relay block side as shown.
FuseCheck forTester ConnectionConditionSpecified value
ABS NO. 1Voltage2±GroundConstantBattery voltage
AM14±Ground
ALT5±Ground
MAIN7±Ground
AM29±Ground
ABS NO. 211±Ground
INT13±Ground
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BODY ELECTRICAL SYSTEM Power SourceBE±21
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FuseCheck forTester ConnectionConditionSpecified value
HTRVoltage(15)±GroundConstantBattery voltage
DEF(17)±Ground
DOME(24)±Ground
EFI(26)±Ground
HAZ±HORN(28)±Ground
RADIO NO. 1(30)±Ground
TEL(32)±Ground
ALT±S(34)±Ground
TRAC(36)±Ground
HEAD (RH±LWR)(38)±GroundLight control switch turned to TAIL or
HEAD (LH±LWR)(40)±GroundHEAD and *ENGINE running
HEAD (RH±UPR)(44)±GroundLight control switch turned to HEAD and
HEAD (LH±UPR)(46)±Grounddimmer switch turned to HI or FLASH
If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect the circuits connected to other parts.
2. INSPECT RELAY CIRCUIT Remove the relay from the relay block and inspect the con-
nector on relay block side as shown.
RelayCheck forTester connectionConditionSpecified value
EFIVoltage(4)±GroundConstantBattery voltage
ST(10)±Ground
(11)±Ground
DIM(15)±GroundLight control switch turned to TAIL or HEAD
(16)±Groundand *Engine running
IG2(18)±GroundConstant
HTR(24)±Ground
(25)±Ground
H±LP(28)±Ground
(30)±Ground
DEF(34)±Ground
(35)±Ground
If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect circuits connected to other parts.
BE±22
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BODY ELECTRICAL SYSTEM Power Source
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INSPECTION OF RELAY BLOCK NO. 4
AND NO. 5 RELAY BLOCK
1. INSPECT FUSE CIRCUITRemove the fuse from the relay block and inspect the con-
nector on relay block side as shown.
FuseCheck forTester connectionConditionSpecified value
STHTRVoltage2±GroundIgnition Switch Turn to ONBattery voltage
If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect the circuits connected to other parts.
2. INSPECT RELAY CIRCUIT
Remove the relay from the relay block and inspect the con-
nector on junction block side as shown.
RelayCheck forTester connectionConditionSpecified value
HORNVoltage(8)±GroundConstantBattery voltage
IG MAIN(9)±Ground
(13)±GroundContinuity
CRNRNG LP(14)±GroundIgnition Switch Turned to ONBattery voltage
(15)±Ground
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BODY ELECTRICAL SYSTEM Power SourceBE±23
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If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect the circuits connected to other parts.
INSPECTION OF RELAY BLOCK NO. 6
(ABS and TRAC Relay Block)
INSPECT RELAY CIRCUIT
Remove the relay from the relay block and inspect the con-
nector on junction block side as shown.
RelayCheck forTester connectionConditionSpecified value
TRAC SOLVoltage(1)±GroundConstantBattery voltage
TRAC MTR(7)±Ground
ABS SOL(11)±Ground
ABS MIR(17)±Ground
If the circuit is not as specified, refer to BE±15 wiring diagram
and inspect circuits connected to other parts.
BE±24
±
BODY ELECTRICAL SYSTEM Power Source
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