Toyota Sequoia (2005). Manual - part 551

I28476

R6 
Light Control 
Rheostat Assy

Radio Receiver Assy

J/C

Steering Pad Switch

Spiral Cable 
Sub–assy

From 
TAILLIGHT 
Relay

ILL–

GND

J/C

ILL+

W–G

G

J39

J40

J39

J40

J39

J40

R4

R19

R4

R3

R2

W–G

G

G

G

A

B

A

A

A

B

ILL–

T

12

5

2

10

6

A–1

A–10

C9–1

BR–W

C9–10

(*1)

*1: Separate Type Amplifier
*2: Built–in Type Amplifier

(*2)

(*1) (*2)

6

4

–

DIAGNOSTICS

AUDIO SYSTEM

DI–1999

2193

Illumination circuit

CIRCUIT DESCRIPTION

Power is supplied to the radio receiver panel illumination when the light control switch is in the TAIL or HEAD
position. The body ECU determines the external brightness based on the brightness level detected by the
automatic light control sensor, and then operates the tail relay. Power can also be supplied by operating the
relay.
The intensity of the radio receiver panel illumination can be adjusted by the rheostat switch.

WIRING DIAGRAM

DID9X–01

DI–2000

–

DIAGNOSTICS

AUDIO SYSTEM

2194

INSPECTION PROCEDURE

NOTICE:
The vehicle is equipped with SRS (Supplemental Restraint System) such as airbags. Before servic-
ing (including removal or installation of parts), be sure to read the precautionary notice for the sup-
plemental restraint system (See page 

RS–1

).

1

Check illumination.

CHECK:
Check if the illumination for the radio receiver assy, steering pad switch assy or others (A/C switch, cigarette
lighter, etc.) comes on when the light control switch is turned to the HEAD or TAIL position.
RESULT:

Components with illumination

Go to step

Illumination comes on for all components except radio receiver assy.

A

Illumination comes on for all components except steering pad switch does not

come on.

B

Illumination comes on for all components except radio receiver assy, steering

pad switch, Rear heater control panel, each switch, etc.

C

All illumination does not come on. (Radio receiver assy, steering pad switch,

Combination meter, Rear heater control panel, each switch, etc.)

D

HINT:
If the illuminations have malfunctions, check the rheostat switch.

B

Go to step 4.

C

Go to step 8.

D

Go to combination meter system 
(See page 

DI–1645

).

A

I28739

Separate Type Amplifier 
Wire Harness View:

R4

ILL+

I28743

Built–in Type Amplifier 
Wire Harness View:

R2

ILL+

–

DIAGNOSTICS

AUDIO SYSTEM

DI–2001

2195

2

Check radio receiver assy (ILL+).

PREPARATION:
Disconnect the radio receiver assy connector.
CHECK:
Measure the voltage according to the value(s) in the table be-
low.
OK:

Symbol

(Tester connection)

Condition

Specified condition

ILL+ (R2–10) – 

Body ground (*2)

Light control switch TAIL

10 to 14 V

ILL+ (R4–2) – 

Body ground (*1)

Light control switch TAIL

10 to 14 V

*1: Separate Type Amplifier
*2: Built–in Type Amplifier

NG

Repair or replace harness or connector 
(Radio receiver assy – battery).

OK

I28739

Separate Type Amplifier 
Wire Harness View:

ILL–

R4

I28744

Built–in Type Amplifier 
Wire Harness View:

R3

ILL–

I28577

Light Control Rheostat 
Wire Harness View:

R6

ILL–

DI–2002

–

DIAGNOSTICS

AUDIO SYSTEM

2196

3

Check harness and connector (Radio receiver assy – Light control rheostat).

PREPARATION:
Disconnect the radio receiver assy connector and light control
rheostat connector.
CHECK:
Measure the resistance according to the value(s) in the table
below.
OK:

Symbol (Tester connection)

Specified condition

ILL– (R3–5) – ILL– (R6–6) (*2)

Below 1 

Ω

ILL– (R4–12) – ILL– (R6–6) (*1)

Below 1 

Ω

ILL– (R6–6) – Body ground (*1)

10 k

Ω

 or higher

*1: Separate Type Amplifier
*2: Built–in Type Amplifier

NG

Repair or replace harness or connector.

OK

Replace radio receiver assy.