1991 LEXUS SC400 light

Check for Voltage
(a) Establish conditions in which voltage is present at thecheck point.
Example:
(A)±Ignition SW on
(B)±Ignition SW and SW 1 on
(C)±Ignition SW, SW 1 and Relay on (SW 2 off)
(b) Using a voltmeter, connect the negative (±) lead to a good ground point or negative (±) battery terminal and
the positive (+) lead to the connector or component
terminal. This check can be done with a test bulb instead
of a voltmeter.
Check for Continuity and Resistance
(a) Disconnect the battery terminal or wire so there is no voltage between the check points.
(b) Connect the two leads of an ohmmeter to each of the check points.
If the circuit has diodes, reverse the two leads and check
again.
When contacting the negative (±) lead to the diode positive
(+) side and the positive (+) lead to the negative (±) side,
there should be continuity. When contacting the two leads in
reverse, there should be no continuity.
HINT: Specifications may vary depending on the type of tes-
ter, so refer to the tester's instruction manual before perform-
ing the inspection.
Check LED (Light Emitting Diode) in the same manner as that
for diodes.
HINT:
w Use a tester with a power source of 3 V or greater to
overcome the circuit resistance.
w If a suitable tester is not available, apply battery voltage
and check that the LED lights up.
±
BODY ELECTRICAL SYSTEM General InformationBE±5
WhereEverybodyKnowsYourName

(c) Use a volt/ohmmeter with high impedance (10 k/Vminimum) for troubleshooting of the electrical circuit.
Check the Bulb
(a) Remove the bulb.
(b) There s hould be continuity between the respective
terminals of the bulb together with a certain amount of
resistance.
(c) Apply the two leads of the ohmmeter to each of the terminals.
(d) Apply battery voltage and check that the bulb light up.
Check for Short Circuit
(a) Remove the blown fuse and eliminate all loads from the fuse.
(b) Connect a test bulb in place of the fuse.
(c) Establish conditions in which the test bulb comes on.
Example:
(A)±Ignition SW on
(B)±Ignition SW and SW 1 on
(C)±Ignition SW, SW 1 and Relay on (Connect the Relay) and
SW 2 off (or Disconnect SW 2)
(d) D i s c onnect and reconnect the connectors while
watching the test bulb. The short lies between the
connector where the test bulb stays lit and the connector
where the bulb goes out.
(e) Find the exact location of the short by lightly shaking the problem wire along the body.
BE±6
±
BODY ELECTRICAL SYSTEM General Information
WhereEverybodyKnowsYourName

PREPARATION
SST (SPECIAL SERVICE TOOLS)
IllustrationPart No.Part NameNote
09213±31021
Crankshaft Pulley
Puller
For removing steering wheel
RECOMMENDED TOOLS
IllustrationPart No.Part NameNote
09082±00015TOYOTA
Electrical Tester
09041±0030Torx Driver
T30
For removing and installing steering wheel pad and
power window motor
09042±00010Torx Socket
T30For removing and installing steering wheel pad and
power window motor
EQUIPMENT
Part NameNote
Voltmeter
Ammeter
Ohmmeter
Test lead
ThermometerWater temperature sender gauge, Engine oil level, Warning switch, Seat heater
SyphonBrake fluid level warning switch
Oil bathEngine oil level warning switch
Bulb (1.4 W)Coolant level warning ECU
Bulb (3.4 W)Fuel sender, gauge, Seat belt warning relay
Bulb (21 W)Turn signal flasher relay
Dry cell batteryFuel sender gauge
Heat lightSeat heater
Hexagon wrench (6 mm)Power seat
BE±8±
BODY ELECTRICAL SYSTEM Preparation
WhereEverybodyKnowsYourName

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
WhereEverybodyKnowsYourName

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
±
BODY ELECTRICAL SYSTEM Power SourceBE±19
WhereEverybodyKnowsYourName

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
±
BODY ELECTRICAL SYSTEM Power Source
WhereEverybodyKnowsYourName

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
±
BODY ELECTRICAL SYSTEM Power Source
WhereEverybodyKnowsYourName

LIGHTING SYSTEM
BE±28±
BODY ELECTRICAL SYSTEM Lighting System
WhereEverybodyKnowsYourName