1991 LEXUS SC400 wiring

IDENTIFICATION INFORMATION
VEHICLE IDENTIFICATION NUMBER
This number is stamped on the vehicle identification number plate
at the top of the left instrument panel and is also on the certification
regulation label.A: Vehicle Identification Number
B: Vehicle Identification Number Plate
C: Certification Regulation Label
ENGINE SERIAL NUMBER
The engine serial number is stamped on the engine block as
shown.
GENERAL REPAIR INSTRUCTIONS
1. Use fender seat and floor covers to keep the vehicle clean
and prevent damage.
2. During disassembly, keep parts in the appropriate order to facilitate reassembly.
3. Observe the following:
(a) CAUTION: W ork must be started after approx. 20 seconds
or longer from the time the ignition switch is turned to the
ºLOCKº position and the negative (±) terminal cable is
disconnected from the battery (See page AB±2).
(b) B e fo re pe rfo rmin g ele ctrica l wo rk, disc onnect the
negative cable from the battery terminal.
(c) If it is necessary to disconnect the battery for inspection or repair, always disconnect the cable from the negative
(±) terminal which is grounded to the vehicle body.
(d) To prevent damage to the battery terminal post, loosen the terminal nut and raise the cable straight up without
twisting or prying it.
(e) Clean the battery terminal posts and cable terminals with a shop rag. Do not scrape them with a file or other
abrasive object.
(f) Install the cable terminal to the battery post with the nut loose, and tighten the nut after installation. Do not use
a hammer to tap the terminal onto the post.
(g) Be sure the covers for the positive (+) terminal and negative (±) terminal are properly in place.
4. Check hose and wiring connectors to make sure that they are
secure and correct.
IN±4
±
INTRODUCTION Identification Information, General Repair Instructions
WhereEverybodyKnowsYourName

STANDARD VALUE OF ECU TERMINAL
TerminalsSymbolsWiringColorConditionStandardValue
A14±1A14±7B ER W±BIG OFF10 ~ 14 V
A14±2 A14±3MH MCV R±YIG OFF13 ~ 19

A14±4A14±5MFRSMRECG G±RIG OFF13 ~ 19

A14±6A14±7IG+ ER±L W±BIG ON10 ~ 14 V
Body
A14±7 
Ground Body
E 
Ground Body
W±B 
GroundAlwaysBelow 1

A14±8A14±9FACE DEFW Y±LIG OFF13 ~ 19

A14±15A14±7ACC EL±R W±BTurn ignition switch ACC10 ~ 14 V
A12±2 A14±7REOST EW±G W±B
IG ON and turn headlight control SW
to TAIL position.
Turn Rheostat volume from most
right to left position.
Most
: 0 ~ 14 V
Right

Most
: 10 ~ 14 V
Left
A12 3 A14 7WV EBY WB
Start
the
MAX
Temp. Control Switch:
COLDBelow 1 V
A12±3 A14±7WV EB±Y W±Btheen-
gine MAX
Temp. Control Switch:
HOT10 ~ 14 V
A12 4 A14 7MGC ELR WB
Start the
engine andA/C switch ONBelow 1 V
A12±4 A14±7MGCEL±R W±Bengine andpush AUTO
SWA/C switch OFF10 ~ 14 V
A12 5 A14 7TC EL WBIG ONHLC SW
Rheostat Most
:
Volume RightBelow 1 V
A12±5 A14±7TCEL W±BH.L.C. SW
: TAIL positionRheostat Turn
:
Volume Left10 ~ 14 V
A12±6 A14±7TAIL EG W±BTurn the light control switch to TAILposition10 ~ 14 V
A12±7A14±7LV EYW±BIG ONPush blower SW to change
the blower speed from 1 to
10.Speed 1: 10 ~ 14 V

Speed 10: Below 2 V
A12±8 A14±7BLR EB±R W±BIG ONTurn the blower motorBelow 1.5 V
A12±9 A14±7HR EL±W W±B
IG ON
Turn the blower motorBelow 1 V
IG ONDon't turn the blower motor10 ~ 14 V
A12 10 A14 7RDFGR ERY WBIG ON
Rear defogger switch ONBelow 1 V
A12±10 A14±7RDFGR ER±Y W±BIG ONRear defogger switch OFF10 ~ 14 V
A13±1 A14±7IGN EBW±BStart the engine10 ~ 14 V
AC±32±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

WIRING DIAGRAM
±
AIR CONDITIONING SYSTEM TroubleshootingAC±35
WhereEverybodyKnowsYourName

IG Power Source Circuit
CIRCUIT DESCRIPTION
This is the power source for the air conditioner control assembly (contains\
the A/C control assembly)
and servomotor, ect.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage between terminals IG+ and E
of air conditioner control assembly
connector.
Check continuity between terminal E of air
conditioner control assembly and
body ground.
Check HTR fuse.
Check harness and repair and connector be-
tween air conditioner control assembly and
battery
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36).
Check for short in all the harness
and components connected to
the HTR fuse (See attached wir -
ing diagram).
Repair or replace harness or
connector.
AC±70±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

Check voltage between terminals IG+ and E of air conditioner control
assembly connector.
(1) Remove console upper panel.(See pageBO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Measure voltage between terminals IG+ and E of air
conditioner control assembly.
Voltage: 10 ±14 V
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
Check continuity between terminals E of air conditioner control assem-
bly and body ground.
Measure resistance between terminals E of air condi-
tioner control assembly and body ground.
Resistance:1  or less
Repair or replace harness or connector.
Remove HTR fuse from J/B No. 1.
Check continuity of HTR fuse
Continuity
Check HTR fuse.
Check for short in all the harness and
components connected to the HTR fuse
See attached wiring diagram).
Check and repair harness and connector between air conditioner control \
assembly and battery.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±71
WhereEverybodyKnowsYourName

ACC Power Source Circuit
CIRCUIT DESCRIPTION
This circuit supplies power to the air conditioner control assembly (contai\
ns the A/C control assembly).
DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage between terminals ACC of air
conditioner control assembly connector
and body ground.
Check RADIO No. 2 fuse.
Check and repair harness and connector
between air conditioner control assembly
and battery.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36).
Check for short in all the harness
and components connected to
the RADIO No. 2 fuse (See
attached wiring diagram).
AC±72±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName

Check voltage between terminals ACC of air conditioner control
assembly connector and body ground.
(1) Remove console upper panel.(See page BO-111 ).
(2) Remove A/C control assembly with connec±
tors still connected.
(3) Turn ignition switch ON.
Measure voltage between terminals ACC of air
conditioner control assembly connector and body
ground.
Voltage: 10 ± 14 V
Proceed to next circuit inspection shown on matrix
chart (See page AC-36).
Check RADIO No. 2 fuse.
Remove RADIO No. 2 fuse from J/B No. 1.
Check continuity of RADIO No. 2 fuse.
Continuity.
Check for short in all the harness and
components connected to the RADIO No. 2
fuse (See attached wiring diagram).
Check and repair harness and connector between air conditioner control \
assembly and battery.
INSPECTION PROCEDURE
±
AIR CONDITIONING SYSTEM TroubleshootingAC±73
WhereEverybodyKnowsYourName

\
\


\

\
\
Back±up Power Source Circuit
CIRCUIT DESCRIPTION
This is the backup power source for the air conditioner control assembly. Power is supplied even when
the ignition switch is off and is used for diagnostic code memory, etc.
DIAGNOSTIC CHART
WIRING DIAGRAM
Check voltage between terminal B of air
conditioner control assembly connector
and body ground.
Check DOME fuse.
Proceed to next circuit inspection
shown on matrix chart (See page
AC-36
).
Check and repair harness and connector
between air conditioner control assembly
and battery.
Check for short all in the harness
and components connecteds to
the DOME fuse (See attached wiring
diagram)
AC±74±
AIR CONDITIONING SYSTEM Troubleshooting
WhereEverybodyKnowsYourName