stop start LEXUS SC400 1991 Service Workshop Manual
[x] Cancel search | Manufacturer: LEXUS, Model Year: 1991, Model line: SC400, Model: LEXUS SC400 1991Pages: 4087, PDF Size: 75.75 MB
Page 3888 of 4087

149
1K
4 1I
10
B
9B 64 A 12
1
IJ2
2IJ2 1IJ1
6
PARKING
BRAKE SWM42
4 31
5
7
6
23
1 25A
STOP
7. 5A
ST
POTENTIO METER
CRUIS E CONTROL ACTUATOR GN DL
MC
MO
VR3
VR2
VR1
MAGNETIC
CLUTCH
S2 IDL1 OD1
ECT IDL OD VR1 VR2 VR3 MC MO L STP±
N& C STP+
CRUISE CONTROL ECU
STOP
LIGHT
SW
B±W B±W
W
B±W
W
W
G±W BR±Y
R
W±R
W±R
R
BR±Y
R±B
LG±R P
LG
G±R
W
R±L R±B
LG±R P
LG
G±R B±W
W±B
I9
S12
C19
P3C8
FROM POWER SOURCE SYSTEM
(
SEE PAGE 56 )
R±W
B
PKB
ENGINE AND ECT ECU E9 ,E10
I7
EA
IE 2
10
IE2
11
IE2
5
IE2
1
IE2
6
IE2
2
IG1
19
IJ2
9
B (
CANA DA )
(
USA )
R±L
22 23 9 3 24 25 26 12 11 10 16 1
A B IJ2
10
I9
C24 C23
CLUTCH
START SW CRUISE
CONTROL
CLUTCH SW(
A/T )
B±W
BB±W
B±W
B±W
(
A/T )
(
A/T )
1
2
2
21
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Page 3889 of 4087

150
CRUISE CONTROL
CURRENT IS APPLIED AT ALL TIMES THROUGH STOP FUSE TO TERMINAL 1 OF THE CONTROL ECU TERMINAL 2 OF STOP LIGHT
SWITCH, AND ALSO THROUGH THE DOME FUSE TO TERMINAL 15 OF CRUISE CONTROL ECU.
WITH THE IGNITION SWITCH TURNED TO ON, THE CURRENT FLOWS THROUGH GAUGE FUSE TO TERMINAL (A)1 OF COMBINATION
METER AND THE CURRENT THROUGH ECU±IG FUSE FLOWS TO TERMINAL 14 OF CRUISE CONTROL ECU.
WHEN THE IGNITION SWITCH IS ON AND THE CRUISE CONTROL MAIN SWITCH IS TUR\
NED ON, A SIGNAL IS INPUT FROM TERMINAL
15 OF CRUISE CONTROL MAIN SWITCH TO TERMINAL 4 OF CRUISE CONTROL ECU. AS A RESULT, THE CRUISE CONTROL ECU
FUNCTIONS AND THE CURRENT TO TERMINAL 14 OF CRUISE CONTROL ECU TO TERMINAL 13 OF CRUISE CONTROL ECU "
GROUND, AND THE CRUISE CONTROL SYSTEM IS IN A CONDITION READY FOR OPERATION.
AT THE SAME TIME, THE CURRENT THROUGH THE GAUGE FUSE FLOWS FROM TERMINAL (A)1 OF CRUISE CONTROL INDICATOR
LIGHT " TERMINAL (B)20 "TERMINAL 5 OF CRUISE CONTROL ECU "TERMINAL 13 " TO GROUND, CAUSING THE CRUISE
CONTROL INDICATOR LIGHT TO LIGHT UP, INDICATING THAT THE CRUISE CONTROL IS READY FOR OPERATION.
1. SET OPERATION
WHEN THE CRUISE CONTROL MAIN SWITCH IS TURNED ON AND THE SET SWITCH IS PUSHE\
D WITH THE VEHICLE SPEED WITHIN
THE SET LIMIT (APPROX. 40 KM/H, 2.5 MPH TO 200 KM/H, 124 MPH), A SIGNAL IS INPUT TO TERMINAL 18 OF THE CRUISE CONTROL
ECU AND THE VEHICLE SPEED AT THE TIME THE SET SWITCH IS RELEASED IS MEMORIZED IN THE ECU AS THE SET\
SPEED.
2. SET SPEED CONTROL
DURING CRUISE CONTROL DRIVING, THE ECU COMPARES THE SET SPEED MEMORIZED IN THE ECU WITH THE ACTUAL VEHICLE
SPEED INPUT INTO TERMINAL 20 OF THE CRUISE CONTROL ECU FROM THE SPEED SENSOR, AND CONTROLS THE CRUIS\
E
CONTROL ACTUATOR TO MAINTAIN THE SET SPEED.
WHEN THE ACTUAL SPEED IS LOWER THAN THE SET SPEED, THE ECU CAUSES THE CURREN\
T TO THE CRUISE CONTROL
ACTUATOR TO FLOW FROM TERMINAL 12 " TERMINAL 6 OF CRUISE CONTROL ACTUATOR "TERMINAL 7 " TERMINAL 11 OF
CRUISE CONTROL ECU. AS A RESULT, THE MOTOR IN THE CRUISE CONTROL ACTUATOR IS ROTATED TO OPEN THE THROTTLE
VALVE AND THE THROTTLE CABLE IS PULLED TO INCREASE THE VEHICLE SPEED. WHEN THE ACTUAL DRIVING SPEED IS HIGHER
THAN THE SET SPEED, THE CURRENT TO CRUISE CONTROL ACTUATOR FLOWS FROM TERMINAL 11 OF ECU "TERMINAL 7 OF
CRUISE CONTROL ACTUATOR "TERMINAL 6 "TERMINAL 12 OF CRUISE CONTROL ECU.
THIS CAUSES THE MOTOR IN THE CRUISE CONTROL ACTUATOR TO ROTATE TO CLOSE THE THROTTLE VALVE AND RETURN THE
THROTTLE CABLE TO DECREASE THE VEHICLE SPEED.
3. COAST CONTROL
DURING THE CRUISE CONTROL DRIVING, WHILE THE COAST SWITCH IS ON, THE CRUISE CONTROL ACTUATOR RETURNS THE
THROTTLE CABLE TO CLOSE THE THROTTLE VALVE AND DECREASE THE DRIVING SPEED. THE VEHICLE SPEED WHEN THE COAST
SWITCH IS TURNED OFF IS MEMORIZED AND THE VEHICLE CONTINUES AT THE NEW SET SPEED.
4. ACCEL CONTROL
DURING CRUISE CONTROL DRIVING, WHILE THE ACCEL SWITCH IS TURNED ON, THE CRUISE\
CONTROL ACTUATOR PULLS THE
THROTTLE CABLE TO OPEN THE THROTTLE VALVE AND INCREASE THE DRIVING SPEED.
THE VEHICLE SPEED WHEN THE ACCEL SWITCH IS TURNED OFF IS MEMORIZED AND THE \
VEHICLE CONTINUES AT THE NEW SET
SPEED.
5. RESUME CONTROL
UNLESS THE VEHICLE SPEED FALLS BELOW THE MINIMUM SPEED LIMIT (APPROX. 40 KM/H, 25 MPH) AFTER CANCELING THE SET
SPEED BY THE CANCEL SWITCH, PUSHING THE RESUME SWITCH WILL CAUSE THE VEHICLE \
TO RESUME THE SPEED SET BEFORE
CANCELLATION.
6. MANUAL CANCEL MECHANISM
IF ANY OF THE FOLLOWING OPERATIONS OCCURS DURING CRUISE CONTROL OPERATION, THE SAFETY MAGNETIC CLUTCH OF
THE ACTUATOR TURNS OFF AND THE MOTOR ROTATES TO CLOSE THE THROTTLE VALVE AND THE CRUISE CONTROL IS
RELEASED.
* PLACING THE SHIFT LEVER IN ªNº RANGE (NEUTRAL START SWITCH ON)). ªSIGNAL INPUT TO TERMINAL 2 OF ECUº
* DEPRESSING THE BRAKE LEVER (STOP LIGHT SWITCH ON). ªSIGNAL INPUT TO TERMINAL 16 OF ECUº
* PULLING THE PARKING BRAKE PEDAL (PARKING BRAKE SWITCH ON). ªSIGNAL INPUT TO TERMINAL 3 OF ECUº
* PUSHING THE CANCEL SWITCH (CANCEL SWITCH ON). ªSIGNAL INPUT TO TERMINAL 18ª
SYSTEM OUTLINE
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Page 3901 of 4087

66
.
ENGINE CONTROL
THIS SYSTEM UTILIZES AN ECU AND MAINTAINS OVERALL CONTROL OF THE ENGINE, TRANSMISSION AND SO ON. AN OUTLINE O\
F
THE ENGINE CONTROL IS EXPLAINED HERE.
1. INPUT SIGNALS
(1) WATER TEMP. SIGNAL CIRCUITTHE WATER TEMP. SENSOR DETECTS THE ENGINE COOLANT TEMP. AND HAS A BUILT±IN THERMISTOR WITH A RESISTANCE
WHICH VARIES ACCORDING TO THE WATER TEMP. THE WATER TEMP. IS INPUT INTO TERMINAL THW OF ENGINE CONTROL
ECU AS A CONTROL SIGNAL.
(2) INTAKE AIR TEMP. SIGNAL CIRCUIT THE INTAKE AIR TEMP. SENSOR IS INSTALLED IN THE AIR FLOW METER AND DETECTS THE INTAKE AIR TEMP., WHICH IS INPUT
AS A CONTROL SIGNAL TO TERMINAL THA OF ENGINE CONTROL ECU.
(3) OXYGEN SENSOR SIGNAL CIRCUIT THE OXYGEN DENSITY IN THE EXHAUST EMISSION IS DETECTED AND INPUT AS A CONTR\
OL SIGNAL FROM THE OXYGEN
SENSOR NO. 1 AND NO. 2 TO TERMINALS OX1, OX2 OF THE ECU AND FROM THE OXYGEN SENSOR SUB (FOR CALIFORNIA) TO
TERMINAL OX3 OF THE ECU.
TO STABILIZE DETECTION PERFORMANCE BY THE OXYGEN SENSOR SUB (FOR CALIFORNIA)\
IS WARMED. THIS HEATER IS
ALSO CONTROLLED BY THE ECU (HT).
(4) RPM SIGNAL CIRCUIT CRANKSHAFT POSITION IS DETECTED BY THE PICK±UP COIL INSTALLED INSIDE THE DISTRIBUTOR. CRANKSHAFT POSITION
IS INPUT AS A CONTROL SIGNAL TO TERMINALS G1 AND G2 OF THE ECU, AND RPM IS INPUT TO TERMINAL NE.
(5) THROTTLE SIGNAL CIRCUIT THE THROTTLE POSITION SENSOR DETECTS THE THROTTLE VALVE OPENING ANGLE AS A CONTROL SIGNAL, WHICH IS
INPUT INTO TERMINAL VTA1 OF THE ECU. WHEN THE VALVE IS COMPLETELY CLOSED, THE CONTROL SIGNAL IS INPUT INTO
TERMINAL IDL1 .
(6) VEHICLE SPEED CIRCUIT THE VEHICLE SPEED IS DETECTED BY SPEED SENSOR NO. 1 INSTALLED IN THE TRANSMISSION AND THE SIGNAL IS INPUT TO
TERMINAL SPD OF THE ECU VIA THE COMB. METER.
(7) NEUTRAL START SIGNAL CIRCUIT THE NEUTRAL START SW DETECTS WHETHER THE SHIFT POSITION IS IN NEUTRAL OR NOT, AND THE SIGNAL IS INPUT INTO
TERMINAL NSW OF THE ECU.
(8) AIRCONDITIONING SW SIGNAL CIRCUIT THE OPERATING VOLTAGE OF THE A/C MAGNETIC CLUTCH IS DETECTED AND THE SIGNAL IS INPUT INTO TERMINAL ACMG OF
ECU AS A CONTROL SIGNAL.
(9) BATTERY SIGNAL CIRCUIT VOLTAGE IS CONSTANTLY APPLIED TO TERMINAL BATT OF THE ECU. WITH THE IGNITION SW TURNED ON, THE VOLTAGE FOR
ECU START±UP POWER SUPPLY IS APPLIED TO TERMINALS +B AND +B1 OF ECU VIA EFI MAIN RELAY.
THE CURRENT FLOWING THROUGH THE IGN FUSE FLOWS TO TERMINAL IGSW OF THE ECU.
(10) INTAKE AIR VOLUME SIGNAL CIRCUIT INTAKE AIR VOLUME IS DETECTED BY THE AIR FLOW METER AND THE SIGNAL IS INPUT TO TERMINAL KS OF THE ECU AS A
CONTROL SIGNAL.
(11) STOP LIGHT SW SIGNAL CIRCUIT THE STOP LIGHT SW IS USED TO DETECT WHETHER OR NOT THE VEHICLE IS BRAKING AND THE SIGNAL IS INPUT INTO
TERMINAL STP OF THE ECU AS A CONTROL SIGNAL.
(12) STA SIGNAL CIRCUIT TO CONFIRM WHETHER THE ENGINE IS CRANKING, THE VOLTAGE APPLIED TO THE STARTER MOTOR DURING CRANKING IS
DETECTED AND THE SIGNAL IS INPUT INTO TERMINAL STA OF THE ECU AS A CONTROL SIGNAL.
(13) ENGINE KNOCK SIGNAL CIRCUIT ENGINE KNOCKING IS DETECTED BY KNOCK SENSOR NO. 1 AND NO. 2 AND THE SIGN\
AL IS INPUT INTO TERMINALS KNK1 AND
KNK2 AS A CONTROL SIGNAL.
SYSTEM OUTLINE
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Page 3904 of 4087

69
E2022 22
1H
12
2
22
22 1I
10
P
N
3
2
1 2
EB2
1
IE1
15 IJ2
7 IJ1
10 IK1 7
IK1
6
1J
3
1E12
31 23 132
1
4
52 I32
EB1
3 EB2 1
VCC OUT GNDY
L±R
B±O B
Y
B
L±R
W
B±O
B±R B±Y
B±W
B±R B±O
B±W B±O
Y
B
L±R
W
B±O
B±R B±R
B±W
B±O
B
B
B
B±R B±R B±Y
W±B
W Y
R
L±R Y
G±W
G±W B±O B
L±O
B
B
B±WB±Y
R
L±O
NEUTRAL
START SW
FROM POWER SOURCESYSTEM(
SEE PAGE 56 )
FROM POWER SOURCE SYSTEM
(
SEE PAGE 56 )
STARTER
RELAY S3
S12N1
7. 5A
IGN
30A
EFI
15A
STOP10A
GAUGE
SPEED SENSOR NO. 1
EFI MAIN
RELAY
STOP LIGHT
SW
TO THEFT DETERRENT
ANDDOORLOCK
ECU (
ST )
TO STARTER
4
3
B±Y
B±Y EB1
8
G±W
W
2 1 IJ 2
8
1I
5
C23
CLUTCH
START
SW B
B
( A/T )
(
M/T )
(
A/T )
B±W
( M/T ) IJ1
6
(A/T )
EB
W±B
B±W
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Page 3955 of 4087

OVERALL ELECTRICAL WIRING DIAGRAM
1234
1J
7 1J
31J 6 22
1B
4 1I
51K 42 22
22
2
4
ACC
IG1
ST1 IG2
AM1 2
1
6
11 AM2
32
41 3 1
4
2
21
21
21
21
16 IE1
15 IE1 1 EB22
1BT1 2BT1 3BT1
N P
2
3
21
413
6 14
7
9 17 BT1
21 21 BK EB1J
5
1E
12 7
8
4
15
12
13 1
814 25
1
7IJ2 9IK2 IK1
3A
4
3D
13
3B 1A IK1
IK1
2 1 M 3
W
W±R
W± R W
B± Y
B±R B±R B± Y B±Y
B± R
B± R
L±Y
G±W
B±W
B±O
B±O
L±RW
B±R B±Y B
Y
B±O
B±O
B±O
B±O
B±O
B±O
GR ±YB±R B± Y
B± O
G
G
B
L±O
L±O B
R±GP
G
G
W± B GP
R± G
W± B
W± B L±Y
G±W
YY W±B
B±R
B±YB±W
B± W
W± R
B±O B±O
B±O
B± O
B±O
W
W± B
B±R3 4
G±W W± L
LG
B±Y
B±W
G± R G±Y LG
L±Y
B±R
G± Y
G±R
LG
GR±Y
B± O
B±W B± O
B±R
B±RB± Y
R±G L±Y
G±W B
Y
B
B± Y
B±R W
L±R
B± Y LG
GR±Y
R±L
W
TE1 TE2 TT
ENG
OX 2 OX 1VF1
FP +B
5
G
3
B
W
T6TDCL
C3
CHECK CONNE CT OR
E1
CHECK ENGINE WARNI NG
LIGHT[ COMB. METER]
10A
GA UGE
EFI
MAIN
RELAY
30A
EFI
N1
NE UT RA L
ST ART SW
ST ARTER
RE LA Y
F1 6
FUEL PUMP ECU
BATTERY
F15
FUEL PUMP
30A AM2
60A MAIN
120A ALT
100A AM1
30A I NJ
I11
I NJECTOR No. 6 I10
I NJECTOR No. 5 I9
I NJECTOR No. 4 I7
I NJECTOR No. 2 I8
I NJECTOR No. 3 I6
I NJECTOR No. 1
From Starter< 1±3>
To Thef t Deter rent
and Door Loc k ECU
< 17±3> F9
FUSE BL OCK
7. 5A
ST
7. 5A
IGN
40A
IGSW I15
IGNITION SW
Engine Control
2 LEXUS SC300
GR±YB±R
VF2
TE1
W
W± B
B±Y
17 18
1 2345 6789 10
23
22
21
20
19
15
14
13
12
11 16 12 34 56 78
9 10 1112 13 14 1516 1718
AB
CHECK E NGI NE WA RNI NG
LIGHT[COMB. METER] W
C14 C13 6IJ1
1EB2
IJ112
B±R
B± R
E1
3 BR
25
From Stop Light SW
<5±6><4±6>
C1 3
IG±
From Igniter
ºTACº<1±5>
B,C14 A
19
P
BR
1IJ1 IK1
4
3B
4
Power
Source
(
Cont . ne xt pa ge )
Fr om A/C Contr ol
Assembly
< 22±7> < 22±5>
TC A/ C
P±B P±L4
11
11TC
Fr om A/C Contr ol
Assembly< 22±8> P± B G± Y
IG3
3
B±R
Under the center
pillar LH Fro nt s i de o f
left f ender
7
4
2 1IJ28
B B±W
B
C23
CLUTCH
START SW (
A/T )(
M/ T )
7IJ1
3IJ1B±O B±O
(A/ T )
3 EB1B (
M/T )
*1: (
w/ Traction Control )
* 2:
(
w/oTractionControl )
* 3: (
USA Spec. )
* 4:
(
Ex. USA Sp ec. )
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Page 3966 of 4087

567 8
8LEXUSSC300(
Cont ' d )
22 11 4 14 8 1716 23
1B
5
3A
6 3E
3
3B
3 1E
11 3H 12
18 IK2 15 IK2 12 IJ 2 7IO1 8IO1
9IK2 5IK2 4IK2
2IK2 10IK1
23 E BRP
4E
TRCO 1D
BRC 5E
THFA 4D
BRFA 10 D
FRO 3D
FL O 12 D
RRO 5D
RLO 15 D
ABSO 8D
BAT 2E
IG1 6D
TC 16 E
TR5 11 D
IND 14 D
WT 5
K
15 K
1
K
7D P
16 D N
1EPKB
13 IK2 3H
7
From A/ T Indicat or SW
[ NEUTRAL START SW AND
BACK±UP LIGHT]< 3±7> 26 E
BCM
25 EB±
24 EB
11 E A
12 EA±
13 EACM
14 EGND
13 DCS W
3ES1
15 E
BM 2D
STP 21 E
TR2 6E
NE O 8E
VT H 19 E
VSH 10 E
IDL1 22 E
IDL2
6 2
16 IK2
13 IJ1 3H
14
1E
18 3A
2
1J
1
IJ IF EE
213645
BCM B± B A A± ACM 1J
52
3A
4
3D
13 1E
12 2 13 14
5EE1
1
L
To Engine and
ECT ECU< 2±8>
10A
GA U GE 7. 5A
TRAC
From Stop Light SW
<5±6><4±6>
From Trottle Position
Sensor< 2±8>
FromSubThrottlePosition
Sensor< 2±8>
WB±Y
L
V± R
P±G P±L
LG±B LG
Y±B P
R± B
V±W P±B L
V
R
B± R B± R
R±W L
GR
B
R±W GR
L V± W
P±B
WA TC TC ABS W TRC
B±Y
V± R
P±G P±L
LG±B LG
Y±B
P
R±B
R
B±R RR
R±B
B±Y
W
L±R Y
Y
L±R
G±W
Y± RP±L
V±Y
Y±L R
R±B
BR
Y± R
W± B
BR
G
W L
R Y B
B
W± B Y± R
W±B
W±B
W± B
BR L
GR
L
L
P±B
L±Y W
LG±R LG±R W P±B
V± W L±G
W
P±B
P±B
P±B
W±B
R± W
W
B±Y
TS WB
C3
CHECK
CONNECTOR T6
TDCL
(
Total Diagnstic
Communic ation Link )
TRACTION ECU ABS WARNI NG AND
TRACTION OFF INDICATOR
AND TRA CT I ON I NDI CA TOR
LI GHTABS
TRAC OFF
S8
SUB THROTTL E
ACTUATOR
T12
TRACTION CUT SW (
SHI ELDED )
ABS and Traction Control
To Parking Brake SW
(
Canada )
< 21±2>
To Brake Fluide Level SW
( USA )
< 21±2>
To Parking Brake SW
< 21±3>
C1 3 , C14 KL
T1 3 , T1 4 DE 7IJ2
L±R
ABS AND TRACTION ECU TRACTION ECUABS WARNING AND TRACTION OFF INDICATOR AND
TRA CT I ON I NDI CA TOR L I GHT
Right k ick panel Left k ickpanelRea r
side of
cylinder
head LH
G±W
E
E1
20
To Engine and
ECT ECU< 2± 8> BRBR
BR
1234 67891011
14 15 16 17 18 24
512
25 26
20
19 21 22 23 13 12345 7 891011
1214 15 16 17 18 22
6
19 20 21
13 12345678
16
15
14
13
12
11
10
9 12345678
16
15
14
13
12
11
10
9 1234 67891011
14 15 16 17 18 24
512
25 26
20
19 21 22 23 13
A
A2 4 B A2 5 CA26 DT13 DARK GRAY E T1 4 DARK GRAY
12 34 56 78
910 111213 141516 1718
17 18
1 2345 6789 10
23
22
21
20
19
15
14
13
12
11 16
K
C13 L C14 123
456
12
34
F
T 3 BLACK G T4 BLACK
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Page 3975 of 4087

OVERALL ELECTRICAL WIRING DIAGRAM
1234
16 LEXUS SC300
4ACC
IG1
ST1
IG2
AM1 2
1
11 AM2
3A
4
1J
7
1B
5 1J
5
2
1J
5
3C
4
1B
4 1E
12 1K 13 2 1K 4
3E
13A 8
3D
13 1H 10
16 IE1
15 IG1
10 IK1 2IJ2 1IJ2 9IJ2 7IG2
4 3
2 IE2 6 IE2 1 IE2 5 IE2 11 IE2 10 I E2 MEA
IG
1A
C14 A 3F
43E 3
Y
Y
B±R R
W± R R
BR±Y
P
W
G±W
Y± B
P± B R±W
R±LL
W±B
R±B
LG±R P
LG
G±R B±W
Y± B
Y±B
P±B
P±B
R± B
LG±R P
LG
G± R W±R W±R
W
R
W± R R
BR±Y
P
W± L
W W
W±B
W±B
W±B R±L R±L B±W
16
1
20
9
23
22
3
15 10
13
10 4 1115 5
6
1
3 4 18 13 24 25 26 12 11
675
123 MC
MO
VR3
VR2
VR1
GN D
CCS
CMS
PKB
TC
PI
100A AM1
120A ALT
60A MAIN
30A AM2 30A INJ
B BAT T N&C ECT I DL OD SPD STP+ STP± LY±B
3H
12
B
(
US A )
( CANADA )
6
W
4
W± R
BATTERY CRUI SE CONT ROL
INDICATOR LI GHT
[COMB. METER]
T6
TDCL
(Tot al Diagnos tic
Communic ation Link )C3
CHECK
CONNECTOR
F9
FUSE BLOCK
C15
CRUISE
CONTROL SW
[ COMB. SW]CA NCEL
RE SUME/
ACCEL SET/
COAST
MA I N
C8
CRUISE CONTROL ACTUATOR
POTENTIO METER
MAGNETI C
CLUTCH
C1 9
CRUI SE CONT ROL E CU
S12
STOP LIGHT SW From Stop Light SW
<4±6><5±6> Fr om º STOPº Fus e
<4±6><5±6> Fr om Combination Meter
< 21±5>
Fr om Engine and ECT ECU
<3±4> 10A GAUGE
15A ECU±IG 10A DOME 7. 5A ST
B±WB±Y W
40A IGSW
Cruise Control
14
5
47
14
9
Power
Source
C1 2 B , C14 A
TC
A/ D TC
To Parking Brake SW
< 21±2>
13 IG1
P± B
P±B
To Engine and ECT ECU
<3±3> Fr om Engine and ECT ECU
<3±2>8
I15
IGNITION SW
Ins trument panel
br ace LHFront side of
r ight fender
2
1
CRUISE CONTROL INDICATOR
LIGHT[ COMB. METER] 20 B
C12 B VR1 VR2 VR3 MC L
MO
GND
1221
IJ16
IJZ10
B±W
B±W B
B±W B±W
B±W
B±W
B±W
2
(
M/T )
( A/T )
C2 3
CL UTCH
START SW
C24
CRUISE CONTROL
CLUTCH SW
( M/T )
( A/T )
10 11 12 13 17 18 19 20 21 12345 6789
14 15 16
17 18
1 2345 6789 10
23
22
21
20
19
15
14
13
12
11 16
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Page 3990 of 4087

244
Rear Window Defogger
and Mirror Heater
Remote Control Mirror
Seat Heater
Shift Lock
SRS AIRBAG
Starting
Taillight and
Stop Light
Theft Deterrent and
Door Lock Control
Turn Signal and Hazard
Warning Light
Wiper and Washer
Wireless Door Lock
Remote Control
Horn
Ignition
Illumination
Interior Light
Liquid Crystal Inner
Rear View Mirror
Moon Roof
Power Seat
(Driver's)
Power Source
Power Window
PPS (Progressive
Power Steering
Radio and Player
ABS and
Traction Control
Automatic
Air Conditioner
Auto Antenna
Back±Up Light
Cellular Mobile
Telephone
Charging
Cigarette Lighter
Combination Meter
Cruise Control
Headlight and Light Auto
Turn Off (for USA)
Headlight
(for Canada) ECT and
A/T Indicator
4±2 16±2 7±2
3±2 21±2 3±8
14±4
18±2 19±4 (w/o CD Player)
20±8 (w/ CD Player)9±2 8±2
4±7 (for USA)
5±7 (for Canada)11±2
12±311±5 (w/ Driving
Position Memory)11±7 12±1 1±5 13±2
6±2 15±2 14±2
13±2
17±7 7±3 17±2 15±3
1±315±2
Power Tilt and
Power Telescopic12±2
Power Seat (Passengerºs
and Electric Tension Header
5±2 2±2
Cornering Light ABS (Anti±Lock
Brake System)
22±2
Engine Control Unlock and Seat
Belt Warning
1±2
23±2 (w/o Driving
Position Memory)
1 23±119±2 (w/o CD Player
20±2 (w/ CD Player
14±310±2 (w/ Memory)
5±7 (w/o Memory)
4±3 (for USA)
5±3 (for Canada) 4±5 (for USA)
5±5 (for Canada)
OVERALL ELECTRICAL WIRING DIAGRAM
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Page 3991 of 4087

44
POWER SOURCE (Current Flow Chart)
The chart below shows the route by which current flows from the battery to \
each electrical source
(Fusible Link, Circuit Breaker, Fuse, etc.) and other parts.
The next page and following pages show the parts to which each electrica\
l source outputs current.
Taillight
Relay (Point Side)
30A AM260A MAIN 50A DEFOG
60A HEATER
7.5 TRAC
40A IG SW
120A ALT
Starter Relay
(Point Side)
Headlight Relay
(Point Side)
30A EFI
15A TEL
10A DOME
20A RADIO No. 1
25A HAZ±HORN
Theft Deterrent and
Door Lock ECU
15A HEAD RH
(USA) 15A HEAD LH
(USA)
Dimmer Relay
(Coil Side)
Starter
15A STOPIgnition SW
(AM1)
30A DOOR
15A TAIL
Alternator
ABS Motor Relay
(Point Side)
Defogger
Relay
Starter ABS
Actuator
10A MIR±HTR
15A ECU±B 7.5A PANEL
7.5 IGN
Engine ECU Traction Brake
Actuator
30A INJ
60A ABS No.1
Traction Brake
Main Relay
(Point Side)
ABS
Actuator Relay
30A POWER
Integration
Relay
100A AM1
Seat Heater
Relay (Point Side)
7.5 ALT SENCING
30A ABS No.2 Headlight
Relay
(Coil Side)
Traction Motor
Relay (Point Side)Traction Pump
and Motor Dimmer Relay
(Point Side) Ignition SW
(AM2)
Taillight
Relay (Coil Side)
15A HEAD (LH±LWR)
(CANADA)
15A HEAD (RH±LWR)
(CANADA)
Engine and
ECT ECU
15A HEAD (LH±UPR)
(CANADA)
15A HEAD (RH±UPR)
(CANADA) ABS and
Traction ECU
Battery
[LOCATION](1): J/B No. 1 (See page
20)(2): R/B No. 2 (See page 19)(3): R/B No. 4 (See page 23)
20
19 22
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Page 3996 of 4087
![LEXUS SC400 1991 Service Workshop Manual
49
F16 F18 I1H8
G2
G1 H1 H3 H2 H4 H5 I2 I14 I15 L7 I16 L2 M2L6
L3 M4
80
194
111 94 101
62
68
101 11 2
126
186 154
162
68 68 94
216
90 86
107
H6 H7 H9 98
N1
Unlock Warning SW
[Ignition SW] Igniter No. LEXUS SC400 1991 Service Workshop Manual
49
F16 F18 I1H8
G2
G1 H1 H3 H2 H4 H5 I2 I14 I15 L7 I16 L2 M2L6
L3 M4
80
194
111 94 101
62
68
101 11 2
126
186 154
162
68 68 94
216
90 86
107
H6 H7 H9 98
N1
Unlock Warning SW
[Ignition SW] Igniter No.](/img/36/57051/w960_57051-3995.png)
49
F16 F18 I1H8
G2
G1 H1 H3 H2 H4 H5 I2 I14 I15 L7 I16 L2 M2L6
L3 M4
80
194
111 94 101
62
68
101 11 2
126
186 154
162
68 68 94
216
90 86
107
H6 H7 H9 98
N1
Unlock Warning SW
[Ignition SW] Igniter No.1 Fuel Pump ECU
Glove Box Light
Headlight LH HI
Hazard SW
High Mount Stop Light
(w/ Rear Spailer) Horn LHISC ValveIgnition Key Cylinder Light
Key Inter Lock Solenoid
Moon Roof Control Relay Light Failure Sensor
Luggage Compartment
Light SW
A/T Indicator SW
Back±Up Light SW
Neutral Start SW Licence Plate Light Integration Relay Fuel Sender
Glove Box Light SW
Headlight RH HI
Headlight LH LO
Headlight RH LO
Horn RH
High Mount Stop Light
(w/o Rear Spailer)
Luggage Compartment
Light SW
Moon Roof Motor
86
98
108
182
216
82
91
94
102
82
216 90
104
(4)
: R/B No. 5 (See page ) 22
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