1991 LEXUS SC300 headlight bulb

(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

(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

(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

Troubleshooting
Taillight System
You will find the cause of troubles more easily using the table well shown \
below. In this table, the numbers indi-
cate the order priority of the causes in troubles. Check each part in the o\
rder shown. If necessary, replace the
parts.
See page
BE±4,20BE±20 ,57BE±46BE±49BE±62BE±79BE±4,20
±
BE±6
±
Trouble
Part name
TAIL FuseTaillignt Control RelayLight Control SwitchIntegration RelayLight Failure SensorDoor CourtesyGAUGE FuseWire HarnessBulbOther Parts
Taillight does not light. (Headlight does
not light.) 12 3
SA
Taillight does not light. (Headlight is
normal.)12345
US
A
Only one light does not light. (Taillight) 2 1 U
Rear combination light does not light. 213
ªLight Auto Turn±Off Systemº does
not operate. 1432
Taillight does not light. (Headlight is
does not light.) 123
Taillight does not light. (Headlight is
normal.)12345
Only one light does not light. (Taillight) 21
ARear combination light does not light. 213
ANADA
ªLight Auto Turn±Off Systemº does
not operate. 1423
CA
N
Taillight does not light with light control
SW in TAIL123
Taillight does not go out with light
control SW in OFF1324
Headlight and Taillight do not light with
engine running and light control SW in
OFF
213*14
*1:
Alternator
L
Terminal
BE±58±
BODY ELECTRICAL SYSTEM Lighting System
WhereEverybodyKnowsYourName