Interior dome lights not working properly. Courtesy lights do not time out when doors close and reading lights and dome lights not illuminating. The dome override switch checks out. The Park and Headlamps work properly. The Instrument Panel Dimmer switch works but does not turn on the dome lights at full setting; however, the switch checks out for connecting the dome lamps ( resistance check to wiring).

If the dome lights in your 2009 Cadillac CTS are not turning off, it can be a frustrating issue. Here are some steps to diagnose and potentially fix the problem:
1. **Manually Turn Off the Dome Lights:**
- In most vehicles, including the Cadillac CTS, there's typically a manual switch on or near the dome light itself. Ensure this switch is in the "Off" position.
2. **Check for Open Doors:**
- Make sure all doors, including the trunk and the hood, are completely closed. Sometimes, a door ajar can prevent the dome lights from turning off.
3. **Interior Light Dimmer Control:**
- Check the position of the interior light dimmer control, which is usually located on the headlight switch or dashboard. If it's turned all the way up, it may keep the dome lights on. Adjust it to the lowest setting.
4. **Ignition Switch:**
- Ensure the ignition switch is in the "Off" position. Sometimes, if the ignition switch is left in the "Accessory" position, the dome lights may stay on.
5. **Faulty Door Switches:**
- Each door usually has a door switch that signals the lights to turn on when a door is opened and off when it's closed. One of these switches may be malfunctioning. You can try manually pressing and releasing each door switch to see if the lights respond.
6. **Battery Disconnect and Reconnect:**
- If the above steps don't work, you can disconnect the vehicle's battery for a few minutes and then reconnect it. This can sometimes reset the electrical system and resolve the issue.
7. **Consult the Owner's Manual:**
- Refer to your Cadillac CTS owner's manual for specific information about the dome light controls and troubleshooting tips.
8. **Professional Diagnosis:**
- If the issue persists, it may be related to a more complex electrical problem. In this case, it's advisable to consult a professional mechanic or an auto-electrician to diagnose and repair the problem.
It's important to be patient and methodical when troubleshooting this issue, as it can have various causes. If you're not comfortable working on the electrical system of your vehicle, seeking professional help is a wise choice to avoid further complications.

Interior Lamps
The interior lighting consist of the following 2 groups. This first group includes lamps that may not be dimmed.
• The cargo lamp
• The dome lamps
• The reading lamps
• The vanity mirror lamps
Courtesy Lamps
The courtesy lamps include the reading lamps, cargo lamp, and dome lamps. The cargo lamp and dome lamps may be manually turned ON or OFF by placing the interior lamp switch in the ON or OFF position. When the driver places the dome lamp defeat switch in the OFF position, these courtesy lamps will be disabled. If a door is opened, the courtesy lamps illuminate. After all the doors have been closed, the courtesy lamps will remain illuminated approximately 15 seconds after the last door closes. The courtesy lamps will also turn ON prior to any door being opened and will remain illuminated approximately 40 seconds when the driver removes the ignition key. The body control module (BCM) will immediately turn OFF the courtesy lamps if a door lock command is received with all of the doors closed, or if the ignition switch is turned to either the ON or RUN position.


These lights ?

Vanity Mirror Lamps
The inadvertent power courtesy lamps supply voltage circuit of the body control module (BCM) provides battery positive voltage to each vanity mirror lamp. When the vanity mirror cover on the sunshade is opened, a switch closes to provide a ground circuit and the vanity lamp illuminates.
Battery Rundown Protection/Inadvertent Power
The body control module (BCM) inadvertent power courtesy lamps supply voltage circuit provides battery positive voltage to all of the interior reading lamps and both visor vanity mirror lamps. In the event that any of these lamps were to remain illuminated for a period of more than 20 minutes with the ignition switch in the OFF position, the BCM will deactivate the inadvertent power courtesy lamps supply voltage circuit to prevent a total battery discharge condition. Only when the ignition switch is cycled back to the RUN position will the BCM reset the internal timer and reactivate the inadvertent power courtesy lamps supply voltage circuit.
The BCM also utilizes the inadvertent power courtesy lamps supply voltage circuit as a courtesy lamp request signal circuit when none of the lamps in the circuit are illuminated. When a lamp switch is activated, the BCM receives the request for lamp illumination and switches to supplying voltage to the inadvertent power courtesy lamps supply voltage circuit.

Check fuses under the hood on driver side

Principles of Operation
Interior Lighting The interior lighting is broken down into two groups: the courtesy lamps and the illuminated entry lamps. Both lighting features interact with the courtesy light arbitrator. The battery saver is also listed in this section.
Courtesy Lighting The courtesy lamps consist of the dome lamp and/or map lights. The courtesy lamps can be activated by the GEM using the panel dimmer switch, or by any ajar door. The courtesy lamps will shut off when the doors are closed and the illuminated entry feature is not active, or when the vehicle speed is greater than 8 kph (5 mph). The interior lamps will not be reactivated until the vehicle speed is less than 5 kph (3 mph) and a new door open warning lamp switch signal is received. The inputs are:

• ignition switch position

• driver door ajar switch

• front passenger door ajar switch

• rear left door ajar switch

• rear right door ajar switch

• vehicle speed switch (VSS)

The outputs are:

• battery saver relay

• interior lamp relay

Which of these lamps do not work , ones that can be dimmed or ones that can't ?
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:
• Auxiliary dome lamp (SEO, RPO 6C7)
• Dome lamp
• Inside rear view mirror lamps
• Instrument panel (I/P) courtesy lamps
• Reading lamps
• Rear compartment courtesy lamp
• Sunshade vanity mirror lamps
Battery positive voltage is applied at all times to the driver information center (DIC)/remote keyless entry (RKE) fuse and to the switched side of the BATT RUNDOWN PROTECTION relay in the right I/P junction block. The DIC/RKE fuse supplies battery positive voltage to the coil side of the BATT RUNDOWN PROTECTION relay. When the ignition is turned to the ON position, the body control module (BCM) provides a ground to the courtesy lamp relay control circuit. This energizes the BATT RUNDOWN PROTECTION relay and applies battery positive voltage to I/P BRP fuse and to the TRK/ROOF/BRP fuse. Battery positive voltage is applied from the I/P BRP fuse to the I/P courtesy lamps and to the courtesy lamp supply voltage circuit to the BCM. Battery positive voltage is also applied from the TRK/ROOF/BRP fuse to the:
• Rear compartment courtesy lamp
• Dome lamp
• Inside rear view mirror lamps
• Roof rail/reading lamps assembly
• Sunshade vanity mirror lamps
If the BCM receives a door lock or unlock input signal, the BCM will activate the BATT RUNDOWN PROTECTION relay, which provides battery positive voltage to all interior courtesy lamps. When any door is opened, the door jam switch contacts close and the BCM receives a door-open input signal. The BCM then applies a ground to the interior lamp control circuit and to the courtesy lamp low control circuit illuminating the courtesy and dome lamps.
After all the doors are closed, the courtesy lamps remain illuminated for approximately 40 seconds. The courtesy lamps will also turn on and remain illuminated for approximately 15 seconds after the ignition key is removed, prior to any door being opened.
When the headlamp switch is placed in the DOME position, the BCM receives a ground signal. The BCM then applies a ground to the interior lamps control circuit. This illuminates the dome and roof rail lamps.
The courtesy lamps will normally turn off using the theater dimming feature. The BCM provides a pulse width modulated ground to all courtesy/reading, dome, and inside rear view mirror lamps for the theater dimming feature. The BCM will immediately turn off the courtesy lamps if a door lock command is received with all the doors closed, or if the ignition switch is turned to either the ON or RUN position.
The BCM activates the interior lighting output 15 seconds after receiving the class 2 message "Airbags Deployed" from the SDM. The interior lamps remain activated for 25 minutes.

Hooking up a factory or someother type of professional scan tool an checking for codes in the BCM - body control module could shed some light on the problem .
DTC B2655 Courtesy Lamp Low Control Circuit High
DTC B2654 Courtesy Lamp Low Control Circuit Low
The body control module (BCM) controls the courtesy lamps through the courtesy lamp low control circuit. The BCM grounds the courtesy lamp low control circuit which completes the interior lamps circuit, and the lamps illuminate.
DTC B2618 Courtesy Lamps Supply Voltage Circuit High
The body control module (BCM) controls the instrument panel (I/P) courtesy lamps through the courtesy lamps supply voltage circuit. The BCM grounds the courtesy lamps low control circuit which completes the I/P courtesy lamps ground circuit, and the lights illuminate.
DTC B2617 Courtesy Lamps Supply Voltage Circuit Low

The BCM supplies a ground to turn the lights on . One of the grounds for the BCM could faulty - lose , corroided etc. Looking at factory service info I see two ground points for the BCM - G201 & G203
G201
Under the I/P, to the right of the steering column, on the I/P support bracket

G203
Under the I/P, to the right of the steering column, on the I/P support bracket

could be a problem with the BCM

https://www.corvetteforum.com/forums/c6-corvette-general-discussion/1700828-help-rearview-mirror-lights-won-t-turn-off.html
This forum from corvette may shed some light on what to do.

You mite have a DTC - diagnostic trouble code stored in the BCM - body control module , The BCM controls the interior lights ! Have you heard of a BCM ?
DTC B2615
The body control module (BCM) receives a ground signal from the door jamb, liftglass/liftgate, or courtesy lamp switches requesting courtesy/dome lamp illumination. When this occurs, the BCM directly sends a voltage through the courtesy lamp supply voltage circuit illuminating the courtesy/dome lamps.
Conditions for Setting the DTC
?€¢
When the BCM receives a courtesy lamp illumination request signal and the courtesy lamp supply voltage circuit is shorted to ground.

?€¢
When the BCM is not receiving a courtesy lamp illumination request signal and the courtesy lamp supply voltage circuit is shorted to voltage or open only to the first splice from the BCM.

?€¢
There is a loss of the rear fuse block TBC 3 battery supply voltage to the BCM for more than 1 second

Diagnostic Aids
?€¢
Perform a visual inspection for loose or poor connections at all related components. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.

?€¢
Only an open circuit up to the first splice from the BCM will set DTC B2615.

DTC B3801
The body control module (BCM) monitors the courtesy lamp switch signal circuit in order to determine when the courtesy/dome lamps should be illuminated. When the BCM senses that the courtesy lamp switch signal circuit is grounded when the switch is activated, the BCM will directly illuminate the courtesy/dome lamps. Do you know what a scan tool is ? not a code reader !
Courtesy Lamps Inoperative




GM Tech 2 Training video 1996

all the lights above the dash do not work ?????? DOME light's ??? No light's come on when you open the door or any door ? Wouldn't think all the door ajar switches bad at one time .
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:
• Auxiliary dome lamp (SEO, RPO 6C7)
• Dome lamp
• instrument panel (I/P) compartment lamp
• Inside rear view mirror lamps
• I/P courtesy lamps
• Reading lamps
• Rear compartment courtesy lamp
• Sunshade vanity mirror lamps
Battery positive voltage is applied at all times to the DIC/RKE fuse and to the switched side of the BATT RUNDOWN PROTECTION relay in the right I/P junction block. The DIC/RKE fuse supplies battery positive voltage to the coil side of the BATT RUNDOWN PROTECTION relay. When the ignition is turned to the ON position, the body control module (BCM) provides a ground to the Inadvertent relay control circuit. This energizes the BATT RUNDOWN PROTECTION relay and applies battery positive voltage to I/P BRP fuse and to the TRK/ROOF/BRP fuse. Battery positive voltage is applied from the I/P BRP fuse to the I/P courtesy lamps, I/P compartment lamp and to the I/P compartment feed circuit to the BCM. Battery positive voltage is also applied from the TRK/ROOF/BRP fuse to the:

If the BCM receives a door lock or unlock input signal, the BCM will activate the BATT RUNDOWN PROTECTION relay, which provides battery positive voltage to all interior courtesy lamps. When any door is opened, the door jam switch contacts close and the BCM receives a door-open input signal. The BCM then applies a ground to the theater dimming ground control circuit illuminating the courtesy and dome lamps.
After all the doors are closed, the courtesy lamps remain illuminated for approximately 40 seconds. The courtesy lamps will also turn on and remain illuminated for approximately 15 seconds after the ignition key is removed, prior to any door being opened.
When the headlamp switch is placed in the DOME position, the BCM receives a ground signal. The BCM then applies a ground to the theater dimming ground control circuit. This illuminates the dome and roof rail lamps.
The courtesy lamps will normally turn off using the theater dimming feature. The BCM provides a pulse width modulated ground to all courtesy/reading, dome, and inside rear view mirror lamps for the theater dimming feature. The BCM will immediately turn off the courtesy lamps if a door lock command is received with all the doors closed, or if the ignition switch is turned to either the ON or RUN position.
The BCM activates the interior lighting output 15 seconds after receiving the class 2 message "Airbags Deployed" from the sensing and diagnostic module (SDM). The interior lamps remain activated for 25 minutes.

The door ajar switch is part of the lock actuator inside the door !

Don't think you have a door ajar switch problem , more then like the lighting control module is the culprit . Does the door ajar light on the instrument cluster stay lit ?
The interior lighting can be separated into two distinct modes of operation: the courtesy lighting and the demand lighting. The lighting control module (LCM) controls all of the interior lighting in the vehicle, as described in the following text.
The front dome lamps, rear reading lamps, and instrument panel courtesy lamps, can be illuminated either by opening any of the vehicle doors (courtesy lamp function) or by depressing the headlamp switch (demand lamp function).
When any door is open, the door ajar switch grounds an input to the LCM which then sends power to the courtesy lamps. The voltage sent to the courtesy lamps gradually increases from 0 volts to 12 volts within 500 ms (± 50 ms), to achieve the theater lighting effect. When the door(s) are closed the door ajar switch(es) break(s) the ground to the LCM input which then gradually reduces the power from 12 volts to 0 volts within 5 seconds. (± .5 second).
When the headlamp switch is depressed it grounds an input to the LCM which in turn sends 12 volts to the front dome lamps, rear reading lamps, and instrument panel courtesy lamps. When the headlamp switch is depressed a second time, it breaks the ground to the LCM input which then ceases to send power to the front dome lamps, rear reading lamps, and instrument panel courtesy lamps.

The battery saver will disrupt power to the courtesy lamps after 10 minutes, the demand lamps after 30 minutes, and the headlamps after 10 minutes. Turning the ignition switch to the RUN or ACC position will terminate the battery saver feature by disabling the interrupt timers and reinstate power to the lamps.
Do you know what DTC'S are ? diagnostic trouble codes !
LCM Diagnostic Trouble Code (DTC) Index DTC Description Source Action B1322 Driver Door Ajar Circuit Short to Ground LCM Go To Pinpoint Test F . B1442 Door Handle Switch Circuit Failure LCM Go To Pinpoint Test G . B1445 Door Handle Switch Circuit Short to Ground LCM Go To Pinpoint Test G . B1563 Door Ajar Circuit Failure LCM Go To Pinpoint Test C . B1566 Door Ajar Circuit Short to Ground LCM Go To Pinpoint Test H . B1685 Lamp Dome Input Circuit Failure LCM Go To Pinpoint Test I . B1687 Lamp Dome Input Circuit Short to Battery LCM Go To Pinpoint Test I . - All Other DTCs LCM REFER to Section 419-10 .

PINPOINT TEST C: THE COURTESY LAMPS STAY ON CONTINUOUSLY CONDITIONS DETAILS/RESULTS/ACTIONS C1 CHECK THE SYSTEM OPERATION Open and close each door, making sure that each door is completely closed.

• Are the courtesy lamps still illuminated after the 25 second time-out period?

Yes GO to C2 .

No The system is operating correctly. C2 TEST DOME LAMP SWITCH Depress the dome lamp switch.

• Are the courtesy lamps still illuminated?

Yes DEPRESS the dome lamp switch a second time. GO to C3 .

No The system is operating correctly. C3 CHECK THE LIGHTING CONTROL MODULE
LCM C2145a

• Are the courtesy lamps still illuminated?

Yes REPAIR circuit 53 (BK/LB). REPEAT the self-test. CLEAR the DTCs.

No INSTALL a new LCM. REFER to Section 419-10 . REPEAT the self-test. CLEAR the DTCs.

The interior lamps system consists of 2 main features. Illuminated entry and a battery saver feature that will turn the interior lights off after 20 minutes if they are left On with all doors closed and the ignition Off. The body control module (BCM) controls both of these functions. Battery power is supplied by the BCM through CKT 1732 to the following lamps:
• The dome lamp
• The map lamps
• The rear reading lamps
• The rear dome lamp
• The cargo lamp
• The glove compartment lamp
• The courtesy lamps
• The sunshade lamps
The BCM also controls the ground circuit side of the dome lamp and reading lamps for illuminated entry. The dome lamp and reading lamp will remain on for 20 seconds after the ignition key is removed and the last door is closed. In addition, if the vehicle is equipped with remote keyless entry (RKE), the dome and reading lamps will turn On and stay on for 20 seconds after an UNLOCK signal is received from the keyless entry transmitter.
The reading lamps, dome lamp and map lamps can be turned On at any time by moving the appropriate switch to the On position.
The rear dome lamp is fed battery voltage through CKT 1732 from the BCM, through the liftgate ajar switch, and is grounded through CKT 650 to the rear ground splice pack. The rear dome lamp will turn on when the liftgate is opened. The cargo lamp is fed battery voltage through CKT 1732 from the BCM, through CKT 744 and grounded through the decklid ajar switch.
The courtesy lamps are fed battery power through CKT 1732 and are grounded through CKT 745-- left front, CKT 747--left rear, CKT 748--right rear, CKT 746--right front. These circuits will ground through the door jamb switches. The courtesy lamp will be illuminated when the affected door is opened. For example, when the right rear door is opened, the right rear door courtesy lamp will turn on.

Not a fuse problem , if the BCM had blown fuse other thing's wouldn't be working as well . . Probably wiring or BCM . Using factory diagnostic,s instead of guessing as to what the problem is , is the proper way .

Interior Lamps Diagnosis
Symptom
Procedure
Important: Before proceeding with these diagnostics, check for DTCs. If DTCs are present, complete the associated diagnostics. If the condition still exists, return to this chart.
All of the interior lamps are inoperative when any door is opened.
Chart 1
The dome lamp is inoperative in the ON position, but OK in the door position. The map lamps operate normally.
The dome lamp switch is faulty. Replace the dome lamp switch.
The dome lamp is inoperative in the DOOR position, but is OK in the ON position.
Chart 2
The dome lamp is inoperative in any position and both reading lamps are inoperative.
Disconnect the dome lamp connector (BLK 3-way).
Check for voltage at terminal "C" CKT 1732 ORN wire.
If OK, the dome/map lamp is faulty. If no voltage is present, there is an OPEN in CKT 1732.
Either the right or the left sunshade mirror lamp is inoperative.
Chart 3
Either the right or the left rear reading lamp is inoperative in the ON or the DOOR position.
Chart 4
The rear reading lamp is inoperative in the ON or the DOOR position.
Chart 5
Battery rundown protection is shorted to ground - B1482.
B1482
The left rear reading lamp is inoperative in the ON or the DOOR position.
Chart 6