Lexus SC300 / Lexus SC400. Manual — part 207

(HEADLIGHT SYSTEM)
Description – Headlight System

The component parts of this system and their function are described in the following table.

Parts Name

Function

Light Control Switch

Grounds current from the headlight control relay and taillight control relay via the
integration relay, switching each relay and supplying current to the appropriate bulbs
accordance with the switch position.

Dimmer Switch

Grounds current from the dimmer relay in accordance with the switch position, turning
on the ”LO–Beam” or ”HI Beam” lights. In the case of ”FLASH” it turns the heading
control relay and turns on the ”HI Beam” lights.

Headlight Control
Relay

Turned on by signals from the light control switch, dimmer switch and running light
relay and supplies current to each bulb or headlight dimmer relay.

Headlight
Dimmer Relay

Receives current from the headlight control relay, which switches the relay according
to the position of the dimmer switch and sends current to the headlight ”LO–Beam”
or ”HI Beam”.

Integration Relay

Carries out ”Light Auto Turn–off” 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’s

Detects when the door is open and sends the appropriate signals to integration relay.
(Light Auto Turn–Off System)

Parking Brake
Switch
(CANADA)

Detects when the parking brake lever is released and sends the appropriate signals to
daytime running light relay.

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BODY ELECTRICAL SYSTEM

Lighting System

BE–29

System Description – Headlights

DAYTIME RUNNING LIGHT SYSTEM

The Daytime Running Light (DRL) system is activated when engine is started (However, if the parking brake
lever is engaged when the engine is started, the DRL will not light up after the engine has started. Once the
parking brake is released, the DRL will then light up and will remain on regardless of operation of the parking
brake lever).
The DRL remain on until the ignition switch is turned off.

BE–30

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BODY ELECTRICAL SYSTEM

Lighting System

Operation example (Current flow table)

1.

Daytime Running Light Lights Up

Switch

Position

Ignition switch

ON (Engine running)

Light Control Switch

OFF

Headlight Dimmer Switch

LO or HI

Condition: Battery Voltage

→

(3) , (14)

2.

Taillight Lights Up

Switch

Position

Ignition Switch

OFF or ON

Light Control Switch

TAIL

Headlight Dimmer Switch

LO or HI

Condition: Battery Voltage

→

(3)

Continuity

(16)

→

(17)

→

Ground

3.

Headlight LO–Beam Lights Up

Switch

Position

Ignition Switch

OFF or ON

Light Control Switch

HEAD

Headlight Dimmer Switch

LO

Condition: Battery Voltage

→

(3)

Continuity (16)

→

(17)

→

Ground

(18)

→

(17)

→

Ground

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BODY ELECTRICAL SYSTEM

Lighting System

BE–31

4.

Headlight HI–Beam Lights Up

Switch

Position

Ignition Switch

OFF or ON

Light Control Switch

HEAD

Headlight Dimmer Switch

HI

Condition: Battery Voltage

→

(3)

Continuity (20)

→

(21)

→

Ground

(18)

→

(17)

→

Ground

(16)

→

(17)

→

Ground

5. Headlight

Flash

Switch

Position

Ignition Switch

OFF or ON

Light Control Switch

OFF or TAIL or HEAD

Headlight Dimmer Switch

FLASH

Condition: Battery Voltage

→

(3)

Continuity (19)

→

(21)

→

Ground

(20)

→

(21)

→

Ground

BE–32

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BODY ELECTRICAL SYSTEM

Lighting System