1991 LEXUS SC400 relay

IGNITION SWITCH
Description
The ignition switch is supplied with power from the battery via a fusible l\
ink. Power is supplied to each fuse
and relay according to the position of the switch, whether ªCCº ``ONº or ªSTARTº. The key unlock warning
switch, which detects the set condition of the key, is built into this switch.
Parts Location
Wiring and Connector Diagrams
±
BODY ELECTRICAL SYSTEM Ignition SwitchBE±25
WhereEverybodyKnowsYourName

(HEADLIGHT SYSTEM)
Description ± Headlight System
The component parts of this system and their function are described in the \
following table.
Parts NameFunction
Light Control SwitchGrounds current from the headlight control relay and taillight control r\
elay via the
integration relay, switching each relay and supplying current to the appropriate bulbs
accordance with the switch position.
Dimmer SwitchGrounds current from the dimmer relay in accordance with the switch posi\
tion, turning
on the ºLO±Beamº or ºHI Beamº lights. In the case of º\
FLASHº it turns the heading
control relay and turns on the ºHI Beamº lights.
Headlight Control
RelayTurned on by signals from the light control switch, dimmer switch and run\
ning light
relay and supplies current to each bulb or headlight dimmer relay.
Headlight
Dimmer RelayReceives current from the headlight control relay, which switches the relay according
to the position of the dimmer switch and sends current to the headlight \
ºLO±Beamº
or ºHI Beamº.
Integration RelayCarries out ºLight Auto Turn±offº of the headlights and taillights and cuts off current to
the light control switch in accordance with signals from the GAUGE fuse \
and courtesy
switch.
Door Courtesy
Switch/Driver 'sDetects when the door is open and sends the appropriate signals to integ\
ration relay.
(Light Auto Turn±Off System)
Parking Brake
Switch
(CANADA)Detects when the parking brake lever is released and sends the appropria\
te signals to
daytime running light relay.
±
BODY ELECTRICAL SYSTEM Lighting SystemBE±29
WhereEverybodyKnowsYourName

(Headlight Control Relay)
INSPECTION OF HEADLIGHT CONTROL
RELAY
INSPECT HEADLIGHT CONTROL RELAY(Continuity)
Inspect relay continuity between terminals.
If continuity is not as specified, replace the relay.
(Relay Circuit)
(See page BE±21)
(Headlight Dimmer Relay)
INSPECTION OF HEADLIGHT DIMMER
RELAY
INSPECT HEADLIGHT DIMMER RELAY
(Continuity)
Inspect relay continuity between terminals.
If continuity is not as specified, replace the relay.
BE±48
±
BODY ELECTRICAL SYSTEM Lighting System
WhereEverybodyKnowsYourName

(Integration Relay)
REMOVAL AND INSTALLATION OF
INTEGRATION RELAY
(See page BE±16)
INSPECTION OF INTEGRATION RELAY
INSPECT INTEGRATION RELAY
(Relay Circuit/Light Auto Turn Off System)
Remove the relay from junction block and inspect the con-
nectors on the wire harness and junction block side as shown
in the chart.
(USA)
Check forTester connectionConditionSpecified value
ContinuityA4±GroundPassenger 's CourtesyOFFNo continuityygy
ONContinuity
A5±GroundIgnition KeyPull offNo continuitygy
Put inContinuity
A6±GroundDriver's CourtesyOFFNo continuityy
ONContinuity
A8±GroundSeat BeltUnfastenContinuity
FastenNo continuity
A10±GroundConstantContinuity
B1±GroundPassenger's DoorUnlockContinuityg
LockNo continuity
B2±GroundDriver's DoorUnlockContinuity
LockNo continuity
B3±GroundLight Control SwitchOFFNo continuityg
TAIL or HEADContinuity
B6±GroundLight Control SwitchTAIL or OFFNo continuityg
HEADContinuity
VoltageA1±GroundConstantVoltageg
A2±GroundConstant*Voltage
A7±GroundIgnition SwitchONVoltageg
LOCK or ACCNo voltage
A9±GroundIgnition SwitchONBattery voltageg
LOCK or ACCNo voltage
A11±GroundIgnition SwitchON or ACCVoltageg
LOCKNo voltage
* There is resistance because this circuit is grounded through the bulb.\
±
BODY ELECTRICAL SYSTEM Light SystemBE±49
WhereEverybodyKnowsYourName

(Canada)
Check forTester connectionConditionSpecified value
ContinuityA4±GroundPassenger's CourtesyOFFNo continuityygy
ONContinuity
A5±GroundIgnition KeyPull offNo continuitygy
Put inContinuity
A6±GroundDriver's CourtesyOFFNo continuityy
ONContinuity
A8±GroundSeat BeltUnfastenContinuity
FastenNo continuity
A10±GroundConstantContinuity
A12±GroundConstantContinuity
B1±GroundPassenger's DoorUnlockContinuityg
LockNo continuity
B2±GroundParking Brake
Switch PositionOFF (Switch pin
pushed in)No continuity
ON (Switch pin re-
leased)Continuity
B3±GroundDriver's DoorUnlockContinuity
LockNo continuity
B7±GroundHeadlight Dimmer
Switch PositionLow Beam or High
BeamNo continuity
FlashContinuity
B8±GroundHeadlight DimmerLow BeamNo continuityg
Switch PositionHigh Beam or FlashContinuity
B10±GroundLight Control SwitchOFFNo continuityg
HEAD or TAILContinuity
B12±GroundConstantContinuity
B13±GroundLight Control SwitchOFF or TAILNo continuityg
HEADContinuity
VoltageA1±GroundConstantVoltageg
A2±GroundConstant*Voltage
A7±GroundIgnition SwitchONVoltageg
LOCK or ACCNo voltage
A9±GroundIgnition SwitchON*Voltageg
LOCK or ACCNo voltage
A11±GroundIgnition SwitchON or ACCVoltageg
LOCKNo voltage
B4±GroundEngineSTOPNo voltageg
RunningVoltage
B11±GroundConstantVoltage
* There is resistance because this circuit is grounded through the bulb.\
If the circuit is as specified, trying replacing the relay with a
new one.
If the circuit is not as specified, refer to BE±35 wiring diagram
and inspect the circuit connected to other parts.
BE±50
±
BODY ELECTRICAL SYSTEM Light System
WhereEverybodyKnowsYourName

DEFOGGER SYSTEM
Description
The component parts of this system and their functions are described in the\
following table.
 Parts Name\
 \
Function
 Defogger\
 \
When over current flows in the defogger circuit, the Defogger fuse break\
s the circuit to pro-
tect it against damage.
 


Defogger Relay\
 
\

\

This relay is supplied with current from terminal IG1 of ignition switch\
(Ignition switch
ON) and switches large current from the defogger.
 


A/C Control Panel
Assembly

Defogger Switch\
 
\

\

The defogger switch is built into the A/C Control Panel Assembly. This switch is
supplied with current from the relay and fuse HTR. Grounds current from \
the defogger
relay, turning the defogger relay ON.
 




Defogger

Rear Window
 Outer Mirror\
 
\


\

\

These defoggers generate heat when current is supplied from the defogger\
relay.
Parts Location
±
BODY ELECTRICAL SYSTEM Lighting SystemBE±51
WhereEverybodyKnowsYourName

(c) Turn the defogger switch ON and check that the test bulb andindicator light turn ON, then turn OFF after about 15 minutes.
If operation is not as specified, replace the air conditioner control
panel assembly.
(Defogger Relay)
INSPECTION OF DEFOGGER RELAY
INSPECT RELAY CONTINUITY AND OPERATION
If continuity is not as specified, replace the relay.
(Defogger Wires)
INSPECTION AND REPAIR OF
DEFOGGER WIRES
1. INSPECT DEFOGGER WIRESNOTICE:
w When cleaning the glass, use a soft, dry cloth, and wipe
the glass in the direction of the wire. Take care not to
damage the wires.
w Do not use detergents or glass cleaners with abrasive
ingredients.
w When measuring voltage, wind a piece of tin foil around
the top of the negative probe and press the foil against
the wire with your finger as shown.
(a) Turn the ignition switch ON.
(b) Turn the defogger switch ON.
(c) Inspect the voltage at the center of each heat wire as
shown.
 Voltage Criteria
Approx. 5 VOkay (No break in wire) Approx. 10 V or 0 V Broken wire
HINT: If there is approximately 10 volts, the wire is broken be-
tween the center of the wire and the positive (+) end. If there
is no voltage, the wire is broken between the center of the
wire and ground.
±
BODY ELECTRICAL SYSTEM Defogger SystemBE±53
WhereEverybodyKnowsYourName

(TAILLIGHT SYSTEM)
Description ± Taillight System
The component parts of this system and their function are as shown in the f\
ollowing table.
 Parts Name\
 \
Function
 


Light Control Switch\
 
\

\

Grounds current from the taillight control relay via the integration rel\
ay, switching each relay
and supplying current to the appropriate bulbs accordance with the switc\
h position.
 Taillight Control Relay\
 \
Turned on by signals from the light control switch and supplies current t\
o each bulb.
 




Integration Relay
\
 
\


\

\

Carries out ºLight Auto Turn±Offº of the headlights, fog lights and taillights and cuts off cur-
rent to the light control switch in accordance with signals from the GAU\
GE fuse and door
courtesy switch.
 


Light Failure Sensor\
 
\

\

This sensor senses when a bulb in rear combination light is burnt out an\
d lights up a warning
light.
Integration Relay\
 Integration Relay
(Daytime Running
\
 \

Refer to
BE±30. (y g
Light Relay: CANADA)\
 \

PARTS LOCATION ± Taillight System
±
BODY ELECTRICAL SYSTEM Lighting SystemBE±53
WhereEverybodyKnowsYourName