Radio does not work. When the rear blower is turned on, the lights on the driver panel dim with the blower switch.

Interior Lights Dimming Circuit Description
VF Displays
When the ignition switch is in the RUN position, the instrument cluster activates its VF display. The instrument cluster also coordinates the display illumination for the radio (IRC), the cellular telephone (PHN), and the climate control Panel (CCP) anytime the ignition switch is in the RUN position.
Incandescent Dimming 1 (INC DIM 1)
The INC DIM 1 consists of lamps powered by CKT 8 (GRY). These are referred to as the park lamp backlighting because they are only active if the park lamps are on and the ambient light sensor indicates darkness.
Incandescent Dimming 2 (INC DIM 2)
The INC DIM 2 output is used as a general interior light source and an illuminated entry feature that provides interior lighting. The INC DIM 2 consists of lamps powered by CKT 1244 (BRN). When one or more of the following conditions occur, the INC DIM 2 lamps will be active:
• The interior lamps switch is active.
• The park lamps are on and the ambient light sensor indicates darkness
• The ignition switch is in the RUN position and the ambient light sensor indicates darkness
• A Class 2 message is received from the body control module (PZM) indicating that the courtesy lamps are active.
Dimming
The instrument cluster controls all of the interior dimming functions. The instrument cluster receives an ambient light level input from the ambient light sensor and determines whether it is light or dark. If the ambient light sensor is inoperative, the instrument cluster will assume a condition of darkness. Dimming of the VF displays is only allowed when the ignition switch is in the RUN position, the park lamps are on, and the ambient light sensor indicates darkness. If all conditions for the VF dimming are met, the instrument cluster uses the input from the potentiometer in the headlamp switch to determine the level of dimming. The dimming level is sent to the radio (IRC), the cellular telephone (PHN), and the climate control panel (CCP) via a Class 2 message. These modules then adjust the dimming level of their VF display. The instrument cluster provides dimming control of the incandescent lighting through the INC DIM 1 and INC DIM 2 outputs. The instrument cluster provides dimming control of the electronic PRNDL LED through CKT 1382 (PPL/WHT). The dimming level will very based on the potentiometer in the headlamp switch whenever the parklamps are on and the ambient light sensor indicates darkness, regardless of the position of the ignition switch.


1998 Cadillac DeVille ' DeVille, Eldorado (VIN E/K) Service Manual ' Body and Accessories ' Lighting Systems ' Diagnostic Information and Procedures ' Document ID: 489166
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Interior Lights Dimming System Check
Step
Action
Normal Result(s)
Abnormal Result(s)*
1
Turn the ignition switch to the OFF position.
Place the interior lamps switch in the ON position.
All incandescent lighting on the INC DIM D2 output turns ON. INC DIM 2 includes all of the lighting on CKT 1244 (BRN), which is the backlighting for the headlamp switch and the floodlighting for the vehicle doors.
Incandescent Lamps Inoperative
2
Place the interior lamps switch in the OFF position.
Turn the ignition switch to the RUN position.
INC DIM 2 lighting turns OFF.
All of the VF displays light. VF displays include the following components (if equipped):
• The radio (IRC)
• The cellular telephone (PHN)
• The driver information center (DIC)
• The instrument cluster (IPC)
• The climate control panel (CCP)
• Vacuum Fluorescent Displays Inoperative - All
• Incandescent Lamps Always On
3
Cover the ambient light sensor with the twilight OFF.
Place the headlamp switch in the PARK position.
The park lamps turn ON.
All of the VF displays dim in order to match the current dimming control level. All of the incandescent lighting for INC DIM 1 and INC DIM 2 light at the current dimming control level. INC DIM 1 includes all of the park lamp backlighting on CKT 8 (GRY) which is composed of the following components:
• The radio (IRC)
• The front cigar lighter
• The steering wheel controls
• The driver information center (DIC)
• The climate control panel (CCP)
• The instrument cluster (IPC)
• The heated seat switches
• The auxiliary blower switches
• The ash tray lamps
• The PRNDL lamp
Exterior Lights System Check
4
Rotate the headlamp switch dimming control in both directions.
All of the VF displays and all of the incandescent lighting dim and brighten in response to the headlamp switch dimming control.
Vacuum Fluorescent Displays Do Not Dim with Instrument Panel Dimmer Switch
* Refer to the appropriate symptom diagnostic table for the applicable abnormal result.

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Before you start replacing parts ,need a little more information . Maybe able to save you some time an money . Does the horn work when you push the horn button , does the air bag light stay lit in the instrument cluster ? The button lights for the bottons on the steering wheel are lit by the BCM - body control module . Interior Lamps Dimming
The second group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination and incandescent lamps.
When the ignition switch is turned to the RUN position, the radio's vacuum fluorescent (VF) displays turn on at maximum brightness. When the park lamps are on, all incandescent back lighting turn on at the dimming level indicated by the I/P dimmer switch. At the same time all vacuum fluorescent (VF) displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the BCM. When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all vacuum fluorescent (VF) displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.
The following switches and components have back lighting when the park lamps are on:
• The instrument panel cluster (IPC)
• Radio, front and rear
• Window and heated seat switches
• Garage door opener switch
• Selectable ride switch
• Roof beacon switch
• Power take off (PTO) switch
• Headlamp leveling switch
• Rear wheel steering mode select switch
• HVAC control assembly
• Headlamp and panel dimmer switch
• Transfer case shift control switch
• PSIR disable switch
• PRNDL lamps
• Traction control switch
• Steering wheel control switches
• Fog lamp switches

Could be the clock spring inside the steering coulmn ,under the steering wheel if horn doesn't work ,air bag light lit etc...

. The illumination is controlled by the BCM - body control module .
Interior Lamps Dimming
This group includes lamps which may dim. This group may use a combination of vacuum fluorescent (VF) illumination and incandescent lamps.
• HVAC control module, head assembly
• Rear HVAC control module, head assembly
• Radio
• Rear seat Audio
• The instrument panel cluster (IPC)
• The PRNDL lamp, with the exception of the current gear select position
• Power window switches
• Various switches
When the ignition switch is turned to the ON position, the VF display, radio, turns ON at maximum brightness. When the park lamps are ON, all incandescent back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. When the headlamp switch is placed in the PARK position, the park lamp supply voltage circuit provides an input to the body control module (BCM). The BCM then supplies voltage to the I/P dimmer switch through the I/P dimming lamps control circuit. The setting of the I/P dimmer switch determines the amount of voltage that the I/P dimmer switch supplies to the BCM through the I/P dimming lamps low reference circuit. The BCM then sends a pulse width modulation (PWM) voltage to all the interior lamps. All the VF and incandescent back lighting lamps are provided a specific voltage and are then grounded. When the headlight switch is turned to the park lamp or headlamp position, all incandescent back lighting turn ON at the dimming level indicated by the I/P dimmer switch. When the I/P dimmer switch is moved from MIN to MAX, all VF displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.


Do you know what DTC'S - diagnostic trouble codes are ? Codes set in the BCM
DTC B2610 00: Passenger Compartment Dimming 1 Circuit
DTC B2615 00: Passenger Compartment Dimming 2 Circuit
DTC B2652 00: Passenger Compartment Dimming 3
Circuit/System Description
The instrument panel (I/P) lamp dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The I/P dimmer switch provides a voltage signal that will increase as the brightness of the lights are increased and decrease as the brightness of the lights are decreased. The body control module (BCM) provides a low reference signal and a B+ voltage reference to the I/P dimmer switch. When the I/P dimmer switch is placed in the desired position, the dimmed voltage setting is applied from the I/P dimmer switch through the I/P dimmer switch signal circuit to the BCM. The BCM interprets the signal and applies the dimmed voltage to the I/P lamps supply voltage circuit and the interior backlighting components dim to the requested level. Ground for the I/P dimmer switch is provided at G201.

sunroof fuse 1 20amp / power windows - circuit breaker 25 amp
both of these are located in the instrument panel fuse box .

bim or DIM ? the dimmer switch ! Interior Lamps
The interior lamps consists of two groups, lamps that can not be dimmed and lamps that can be dimmed. This first group consists of lamps that may not be dimmed. This includes those lamps that may be manually turned on by placing the interior lamp switch to the DOME position, or by opening a door or a compartment:
• Door courtesy lamps
• Footwell courtesy lamps
• Instrument panel (I/P) compartment lamp
• Overhead console courtesy lamps
• Reading courtesy lamps
• Rear compartment courtesy lamp
• Roof rail courtesy lamps
• Sunshade vanity mirror lamps

Interior Lamps Dimming
This group of interior lighting includes lamps which may be dimmed. This group uses a combination of class 2 controlled illumination and incandescent lamps:
• Air temperature switch
• Cigar lighter lamp
• Door switches
• Driver information center (DIC) switch
• Headlamp switch
• Head-up display (HUD) switch
• Heated seat switches
• HVAC control assembly
• Instrument panel cluster (IPC)
• Memory function switch
• Radio
• Steering wheel controls
• Window switches
For the interior lighting to be dimmed the following conditions must be met:
• A low light level has been detected by the dash integration module (DIM)
• Headlamp switch is placed in to the PARK or HEAD position
• Ignition switch is placed in the ON position
Then all class 2 displays and all incandescent back lighting will be illuminated to the level set by the instrument panel (I/P) dimmer switch. When the I/P dimmer switch is moved from MIN to MAX, all class 2 displays and all incandescent back lighting respond from minimum intensity to maximum brightness.
The DIM supplies battery positive voltage to the coil side of the PRK LP relay in the rear fuse block.
When the I/P dimmer switch is moved from MIN to MAX, then the instrument panel module (IPM), W/CJ2, or climate control panel (CCP), W/C67, applies a message to the class 2 communication circuit to the DIM. The DIM then applies a ground to the park lamp relay control circuit. This energizes the PRK LAMP relay and allows battery positive voltage to be applied through the DIMR fuse to the DIM. The DIM then illuminates the following incandescent lamps through the incandescent dimming output circuit:
• Cigar lighter lamp
• DIC Switch
• Headlamp switch
• HUD switch
• HVAC control assembly
• IPC
• Radio
• Steering wheel controls
The DIM also applies a message to the following class 2 controlled illumination components:
• Drivers door module (DDM)
• HVAC control assembly
• IPC
• Radio
The DDM will then send a message through the simple bus interface (SBI) to the RH front door module (RFDM). The door modules will then illuminate the following components through the incandescent dimming output circuit:
• Air temperature switch
• Heated seat switches (W/KA1)
• Memory function switch (W/A45)
• Power door lock switches
• Power window switches
The ground for these components are provided from the DDM and RFDM.
The following components are grounded at G200:
• Headlamp switch
• HVAC control assembly
• IPC
• Radio
• Steering wheel controls
The following components are grounded at G201:
• Cigar lighter lamp
• DIC Switch
• HUD switch

Fuses are listed here
* = maxi fuse
1*=50A I/P fuse panel
2*=40A blower motor relay
3*= 50A 4 wheel ABS module
4*=20a Main light switch-Instrument cluster
5*=50A Ignition switch, starter relay
6*=20A Transfer case relay
7*= NOT USED
8*=20A Auto Ride Control Switch/on off switch
9*=40A Auto Ride Control relay
10*=30A PCM power relay
mini fuses
1=10A A/C relay
2=20A Aux power point
3= not used
4=15A Fog lamps-Daytime lamps
5=10A Air Bag diagnostic monitor
6=10A Powertrain Control Module (PCM)
7=30A 4WABS module
8=30A PCM relay
9=20A Fuel Pump relay and RAP module
10= 15A Horn relay
11=15A Park Lamp relay-Main Light Switch
12=30A Main light switch--Multi Function switch
13=15A Heated O2 sensors, EGR Vacuum Regulator, EVR solenoid,Camshaft position (CMP) Sensor,
Cannister Vent Solenoid, A4LD Auto Transmission
14=30A Generator-Voltage regulator
Interior fuse panel (mini fuses)
1=7.5A Power mirror switch
2=7.5A Blower motor relay,PAD module,Air Bag diagnostic monitor
3=7.5A Trailer tow connector
4=10A Left headlamp
5=10A Data link connector (DLC)
6=7.5A Air bag diagnostic monitor, Blower motor relay, Passive deactivation Module (PAD)
7=7.5A Trailer Tow connector
8=10A Right headlamp, Daytime running lamps (DRL) module, Foglight relay
9=7.5A Stop Lamp switch
10= 7.5A Speed control-amplifier assembly,Brake pressure switch, Generic electronoc Module (GEM)
Shift lock actuator, Blend door actuator, Main light switch, RABS resistor, A/C heater assembly
Flasher
11= 7.5A Instrument cluster, Main light switch, RABS resistor
12= 10A Power window relay, Washer pump relay
13= 20A Stop lamp switch, Brake pressure switch
14= 20A Rear Anti Lock Brake system (RABS) module
**10A 4WABS module**
15=7.5A Instrument cluster
16= 30A Windshield wiper Motor, Wiper Hi-lo relay, wiper run/park relay
17=7.5A Cig lighter
18=15A Drivers unlock relay-All unlock relay
19=25A PCM power diode
20=7.5A RAP module GEM module, Radio
21=15A Flasher (hazard)
22=20A Aux power socket
23=15A Turn signals
24===not used
25= 7.5A GEM module, Instrument cluster
26= 10A Battery saver relay, Electronic Shift relay, Interior lamp relay
Power window relay,Electronic shift control module, transmission control
27=15A Switch,DRL, Backup lamp switch, DTR sensor,Instrument illumination dimming control module
Dome/map lamp, GEM,electronic shift,Interior lights,Glove box lamp and switch
28=7.5A GEM module-Radio
29= 15A Radio
30=15A Park lamps, trailer Tow relay
31===not used
32=10A rear blower
33=15A Headlamps, DRL module, Instrument cluster
34=7.5A Rear integrated control panel, CD
35=10A RABS test connector
36=7.5A CD, rear integrated control panel, memory seat,

i copied this off another post hope this helps

Does the radio play ? Are any other back lighting components not lighting ? Does the HVAC control panel light up ? You probably need new radio !
The second interior lighting group includes lamps which may be dimmed. This group may use a combination of vacuum fluorescent (VF) illumination, LED illumination and incandescent lamps.
When the ignition switch is turned to the RUN position, the radio VF display turns ON at maximum brightness. When the park lamps are ON, all incandescent and LED back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. At the same time all VF displays dim to match the indicated dimming level. The panel dimmer switch potentiometer is an input to the body control module (BCM). When the driver selects a dimming setting by moving the I/P dimming switch potentiometer, all incandescent back lighting lamps are provided with a specific voltage. When the I/P dimmer switch is moved from MIN to MAX, all VF displays, as well as all incandescent back lighting respond from minimum intensity to maximum brightness in response to the I/P dimmer switch.

Dose

Fuses are listed here

* = maxi fuse

1*=50A I/P fuse panel
2*=40A blower motor relay
3*= 50A 4 wheel ABS module
4*=20a Main light switch-Instrument cluster
5*=50A Ignition switch, starter relay

6*=20A Transfer case relay
7*= NOT USED
8*=20A Auto Ride Control Switch/on off switch
9*=40A Auto Ride Control relay
10*=30A PCM power relay

mini fuses
1=10A A/C relay
2=20A Aux power point
3= not used
4=15A Fog lamps-Daytime lamps
5=10A Air Bag diagnostic monitor
6=10A Powertrain Control Module (PCM)
7=30A 4WABS module
8=30A PCM relay
9=20A Fuel Pump relay and RAP module
10= 15A Horn relay
11=15A Park Lamp relay-Main Light Switch
12=30A Main light switch--Multi Function switch
13=15A Heated O2 sensors, EGR Vacuum Regulator, EVR solenoid,Camshaft position (CMP) Sensor,
Cannister Vent Solenoid, A4LD Auto Transmission
14=30A Generator-Voltage regulator


Interior fuse panel (mini fuses)

1=7.5A Power mirror switch
2=7.5A Blower motor relay,PAD module,Air Bag diagnostic monitor
3=7.5A Trailer tow connector
4=10A Left headlamp
5=10A Data link connector (DLC)
6=7.5A Air bag diagnostic monitor, Blower motor relay, Passive deactivation Module (PAD)
7=7.5A Trailer Tow connector
8=10A Right headlamp, Daytime running lamps (DRL) module, Foglight relay
9=7.5A Stop Lamp switch
10= 7.5A Speed control-amplifier assembly,Brake pressure switch, Generic electronoc Module (GEM)
Shift lock actuator, Blend door actuator, Main light switch, RABS resistor, A/C heater assembly
Flasher
11= 7.5A Instrument cluster, Main light switch, RABS resistor
12= 10A Power window relay, Washer pump relay
13= 20A Stop lamp switch, Brake pressure switch
14= 20A Rear Anti Lock Brake system (RABS) module
**10A 4WABS module**

15=7.5A Instrument cluster
16= 30A Windshield wiper Motor, Wiper Hi-lo relay, wiper run/park relay
17=7.5A Cig lighter
18=15A Drivers unlock relay-All unlock relay
19=25A PCM power diode
20=7.5A RAP module GEM module, Radio
21=15A Flasher (hazard)
22=20A Aux power socket
23=15A Turn signals
24===not used
25= 7.5A GEM module, Instrument cluster
26= 10A Battery saver relay, Electronic Shift relay, Interior lamp relay
Power window relay,Electronic shift control module, transmission control
27=15A Switch,DRL, Backup lamp switch, DTR sensor,Instrument illumination dimming control module
Dome/map lamp, GEM,electronic shift,Interior lights,Glove box lamp and switch
28=7.5A GEM module-Radio
29= 15A Radio
30=15A Park lamps, trailer Tow relay
31===not used
32=10A rear blower
33=15A Headlamps, DRL module, Instrument cluster
34=7.5A Rear integrated control panel, CD
35=10A RABS test connector
36=7.5A CD, rear integrated control panel, memory seat, Message center Attached images __________________

I believe that this is what you are looking for.....
Fuse and relay locations--2nd generation power distribution box Layout- I think this is a good sticky candidate--



Fuses are listed here

* = maxi fuse

1*=50A I/P fuse panel
2*=40A blower motor relay
3*= 50A 4 wheel ABS module
4*=20a Main light switch-Instrument cluster
5*=50A Ignition switch, starter relay

6*=20A Transfer case relay
7*= NOT USED
8*=20A Auto Ride Control Switch/on off switch
9*=40A Auto Ride Control relay
10*=30A PCM power relay

mini fuses
1=10A A/C relay
2=20A Aux power point
3= not used
4=15A Fog lamps-Daytime lamps
5=10A Air Bag diagnostic monitor
6=10A Powertrain Control Module (PCM)
7=30A 4WABS module
8=30A PCM relay
9=20A Fuel Pump relay and RAP module
10= 15A Horn relay
11=15A Park Lamp relay-Main Light Switch
12=30A Main light switch--Multi Function switch
13=15A Heated O2 sensors, EGR Vacuum Regulator, EVR solenoid,Camshaft position (CMP) Sensor,
Cannister Vent Solenoid, A4LD Auto Transmission
14=30A Generator-Voltage regulator


Interior fuse panel (mini fuses)

1=7.5A Power mirror switch
2=7.5A Blower motor relay,PAD module,Air Bag diagnostic monitor
3=7.5A Trailer tow connector
4=10A Left headlamp
5=10A Data link connector (DLC)
6=7.5A Air bag diagnostic monitor, Blower motor relay, Passive deactivation Module (PAD)
7=7.5A Trailer Tow connector
8=10A Right headlamp, Daytime running lamps (DRL) module, Foglight relay
9=7.5A Stop Lamp switch
10= 7.5A Speed control-amplifier assembly,Brake pressure switch, Generic electronoc Module (GEM)
Shift lock actuator, Blend door actuator, Main light switch, RABS resistor, A/C heater assembly
Flasher
11= 7.5A Instrument cluster, Main light switch, RABS resistor
12= 10A Power window relay, Washer pump relay
13= 20A Stop lamp switch, Brake pressure switch
14= 20A Rear Anti Lock Brake system (RABS) module
**10A 4WABS module**

15=7.5A Instrument cluster
16= 30A Windshield wiper Motor, Wiper Hi-lo relay, wiper run/park relay
17=7.5A Cig lighter
18=15A Drivers unlock relay-All unlock relay
19=25A PCM power diode
20=7.5A RAP module GEM module, Radio
21=15A Flasher (hazard)
22=20A Aux power socket
23=15A Turn signals
24===not used
25= 7.5A GEM module, Instrument cluster
26= 10A Battery saver relay, Electronic Shift relay, Interior lamp relay
Power window relay,Electronic shift control module, transmission control
27=15A Switch,DRL, Backup lamp switch, DTR sensor,Instrument illumination dimming control module
Dome/map lamp, GEM,electronic shift,Interior lights,Glove box lamp and switch
28=7.5A GEM module-Radio
29= 15A Radio
30=15A Park lamps, trailer Tow relay
31===not used
32=10A rear blower
33=15A Headlamps, DRL module, Instrument cluster
34=7.5A Rear integrated control panel, CD
35=10A RABS test connector
36=7.5A CD, rear integrated control panel, memory seat, Message center Attached images __________________

Thanks for the FREE help.....NOT! I'm not paying for your service when I can get it for free. You just tried to duped me into joining a pay service when you advertised free solutions...you ****.