Dash display dash "blacks out" when left turn signal engaged. No problems when right engaged or bright/dim headlamp switching. When display comes back it says "Theft System Problem" "car may not restart" "service air bags" (other warnings also) Started noticing drop in displayed voltage prior to isolating left turn signal coincidence Anybody ever experience this type of situation?

Could be the instrument cluster .GM had instrument cluster problems for 2003 to 2006 . Wouldn't think BCM reprogramming to be an issue . Having a qualified repair shop or dealer check for DTC'S - diagnostic trouble codes an view data parmeters would be the first place to start .
When the ignition switch is turned to the RUN position, the instrument panel cluster (IPC), radio VF display, and the HVAC control assembly turns ON at maximum brightness. When the headlamp switch is in the PARK or HEADLAMP ON position, all incandescent and LED back lighting turn ON at the dimming level indicated by the instrument panel (I/P) dimmer switch. The dimmer switch is used to increase and decrease the brightness of the interior backlighting components. The BCM supplies a voltage reference through the I/P dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired brightness position, reference voltage is applied through the dimmer switch rheostat and the I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the I/P lamps supply voltage circuits and the LED dimming supply circuit to all related interior lamps, illuminating them to the desired level of brightness.

DTC B2652
Circuit/System Description
The BCM supplies a voltage reference through the instrument panel (I/P) dimming voltage reference circuit to the interior lamp dimmer switch, which is part of the headlamp switch. When the dimmer switch is placed in a desired position, reference voltage is applied through the dimmer switch rheostat and the I/P lamps dimmer switch signal circuit to the BCM. The BCM interprets this voltage signal, then applies a pulse width modulated (PWM) voltage through the instrument panel lamp supply voltage circuit illuminating the components listed below:
• Headlamp switch
• Instrument panel cluster (IPC)
• Driver and passenger window switches
• Driver and passenger door lock switches
• Outside rearview mirror switch

Circuit/System Testing
Ignition OFF, disconnect the (C2) harness connector at the BCM.
Verify that a test lamp illuminates between the B+ circuit terminal 2 and ground.
? If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal and the B+ circuit fuse is open, test the supply voltage circuits listed below for a short to ground.
• Instrument panel lamp supply voltage circuit terminal 3 C2
• Instrument panel lamp supply voltage circuit terminal 3 C6
Ignition OFF, disconnect all of the instrument panel lamp components fed by the BCM supply voltage circuits listed below.
• Instrument panel supply voltage circuit -terminal 3 C2
• Instrument panel supply voltage circuit -terminal 3 C6
Ignition ON, with a scan tool clear the DTC.
Operate the vehicle within the conditions for running the DTC and verify the DTC does not reset.
? If the DTC resets, test the instrument panel lamp supply voltage circuit for a short to ground. If the circuit test normal, replace the BCM.
Reconnect each component one at a time and verify that the DTC does not reset as current.
? If the DTC resets as current, test or replace the component responsible for setting the DTC.
DTC B3600
DTC B1395 03 : Device Voltage Output 1 Circuit Voltage Below Threshold
DTC B1395 07 : Device Voltage Output 1 Circuit Voltage Above Threshold

Interior Backlighting Malfunction
Diagnostic Fault Information
Circuit
Short to Ground
Open/High Resistance
Short to Voltage
Signal Performance
I/P Dimming Voltage Reference
B1395 03, B3600 03
B1395 03
1, 2
--
Instrument Panel Lamps Dimmer Switch Signal
B3600 03
B3600 03
1, 2
--
Instrument Panel Lamp Supply Voltage
B2652 00
1
1
--
LED Dimming Supply
B2610 00
2
2
--
Headlamp Switch Ground
--
3
--
--
Instrument Panel Lamps Malfunction
LED Malfunction
Headlamps and Dimmer Switch Malfunction

Back lighting or warning lights ? check engine , ABS , air bags , seat belt , oil light etc... ?
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.
• Power window switches
• HVAC control head assembly
• Radio
• The instrument panel cluster (IPC)
When the ignition switch is turned to the ON position, the vacuum fluorescent (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 IP dimmer switch. At the same time all vacuum fluorescent (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 instrument panel dimmer switch through the instrument panel dimming lamps control circuit. The setting of the instrument panel dimmer switch determines the amount of voltage that the instrument panel dimmer switch supplies to the BCM through the instrument panel dimming lamps low reference circuit. The BCM then sends a pulse width modulated (PWM) voltage to all the interior lamps. All the vacuum florescent (VF) and incandescent back lighting lamps are provided a specific voltage and are then grounded. When the headlight switch is turned to the PARK or HEADLAMP position, all incandescent back lighting turn on at the dimming level indicated by the IP dimmer switch. When the IP 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 IP dimmer switch.

I would have it checked for DTC'S - diagnostic trouble codes stored in the BCM !
DTC B2624 Display Dimming Input Range/Performance
The body control module (BCM) supplies voltage to the instrument panel dimmer switch through the instrument panel dimmer switch signal circuit. The dimmer switch varies the voltage and returns the new voltage to the BCM through the dimmer switch signal return circuit. The BCM uses this voltage to determine the illumination level of the instrument panel lamps.

DTC B2625 Display Dimming Pulse Width Modulation (PWM) Output Circuit Range/Performance
The body control module (BCM) receives a variable voltage from the instrument panel (I/P) lamp dimmer switch. The BCM uses this signal in order to vary the illumination level of the I/P lamps. The I/P dimming lamps output from the BCM is a pulse width modulated voltage supply used to light the I/P lamps. If a malfunction occurs in the I/P dimming lamps output circuit, this DTC is set.

DTC B2662 Park Lamp Switch Circuit Malfunction
The park lamps are controlled by the turn/headlamp switch. Positive battery voltage is supplied to the switch through the EXT LP fuse. When the turn/headlamp switch is placed in the park or head position, battery voltage is supplied to the park lamps. The body control module (BCM) is also connected to the park lamp circuit to sense whether or not the park lamps turn ON when the low beam or high beam headlamps are turned ON. The BCM also uses the parklamp battery positive voltage to power the instrument panel (I/P) dimmer output circuit. If the BCM senses that the low beam or high beam headlamps are ON and the park lamp input is not active, DTC B2662 sets.
Do the park lamps work ?

The sensor is usually located on the top of your dashboard. You might see it if you look into your vehicle through your windshield at your dash.
I have seen( one time ) that a gps was bright enough that it caused the dash lights not to come on because the sensor thought it was light outside.
Or you could have gotten a bad sensor.

There are several reasons why your headlamps an running lights don't work , the headlamp switch is a good one ,plus relays an the DIM - dash integrated module an associated wiring ! Here is how the headlamps work , right out of Buick factory service info !
The dash integration module (DIM) provides battery positive voltage to the signal circuits of the headlamp switch. The signal circuits include the headlamp switch headlamps on signal, the flash to pass switch signal and the high beam input. With the headlamp switch in the ON position, a ground path is available for the headlamp switch headlamps on signal circuit of the DIM through the headlamp switch. The DIM provides ground to either the headlamps high beam relay control circuit or the headlamps low beam relay control circuit of the low beam circuit. The position of the headlamp dimmer switch determines which relay control circuit has ground. The DIM supplies battery positive voltage to the relay control circuits, if the headlamps are necessary. The fuse block - underhood supplies battery positive voltage to both relay switch circuits. When the low beam relay control circuit is energized, current flow is to both low beam fuses and to the low beam headlamps. The headlamps have ground at G103 and at G401. When the headlamp high beam relay control circuit is energized, current flow is to both high beam fuses and to the high beam headlamps. The high beam circuit is divided into a left and right side circuit. The current flow of the left high beam is from the fuse to the left high beam lamp. From the lamp, the current flows to the normally-closed contact of the DRL relay to G103. The current flow of the right high beam is from the fuse to the right high beam lamp. From the lamp, the current flow is to ground at G401. When the headlamp dimmer switch lever is pulled toward the driver, the flash-to-pass switch closes. This grounds the DIM flash to pass switch signal circuit. In response to this input, the DIM energizes the HDLP HI BM relay. Both high beams remain on until the driver releases the switch handle. If the low beam headlamps were on during a flash to pass operation, the low beams remain on. The headlights may be switched to high beam with the opposite movement of the headlamp dimmer switch lever.
By running lights , do you mean park lamps or day time running lamps ?
Park, Tail, License and Marker Lamps
The park lamps, including the license lamps, are turned on when the headlamp switch is placed in the PARK or ON position or anytime the headlights are requested. The fuse block - rear supplies battery positive voltage to the switch contacts of the Park LP relay. When the headlamp switch is in PARK or in ON, the park lamp switch on signal circuit of the DIM has a ground path. The DIM provides battery positive voltage to the control circuit of the Park LP relay. When the park lamps and/or the tail lamps are ON, the DIM energizes the park lamp relay control circuit. This closes the switch contacts. Current flows from the Park LP relay to the LH PARK LP and the RH PARK LP fuses. From the fuse, the current flows to the park lamps. The left park lamps are grounded at G103, G401 and G402. The right park lamps and the right tail lamps are grounded at G103 and G401. The DIMR fuse supplies battery positive voltage to the license lamps and to the DIM instrument panel lamp fuse supply voltage - 1 circuit, for interior lamps dimming. The license lamps are grounded at G401.
The best advice I can give is that you take this to a ASE certified professional repair facility unless your a qualified automotive electric repair person !
Diagnostic Starting Point - Lighting Systems
Begin the system diagnosis with the Diagnostic System Check - Lighting Systems . The Diagnostic System Check will provide the following information:
?€¢
The identification of the control modules which command the system

?€¢
The ability of the control modules to communicate through the serial data circuit

?€¢
The identification of any stored diagnostic trouble codes (DTCs) and their status

The use of the Diagnostic System Check will identify the correct procedure for diagnosing the system and where the procedure is located.

The

Without testing i would say you have DRL control module problem , But that would just be a guess .
In the night mode, the DRL ambient light sensor senses darkness. Then, the DRL module turns off the front turn lamps and turns on the headlamps through circuit 10. The DRL module also turns on the park, side marker, license, and tail lamps. If the engine should stall with the DRL control module in the night mode, the DRL control module will turn off the headlamps and leave the side marker, park, license and tail lamps on while the engine is being cranked. The headlamp switch operates as usual.
The Daytime Running Lamps (DRL) control module is designed to automatically operate exterior lights depending on outside light conditions. The DRL control module operates in two modes, the day mode and the night mode. In the day mode, the DRL ambient light sensor senses daylight. Then, the DRL control module turns on the front turn lamps (non-flashing) if under the following conditions:
• The ignition switch is on.
• The headlamps switch is in the OFF position.
• The park brake is released.

The brightness of the Vacuum Fluorescent (VF) displays is controlled by two signals: the park lamps on signal (circuit 230) and the VF dimming signal (circuit 308). With the park lamps on, the VF display of the radio, heater, A/C control (with RPO CJ2) and the instrument cluster will dim for nighttime viewing. When the park lamps on signal is not present (park lamps off), the VF displays are at high brightness for daytime viewing. When the park lamps are on, the I/P lamp dimmer switch provides a signal (VF Dimming Signal circuit 308) which controls the brightness of the VF displays when the I/P lamp dimmer switch is adjusted.

Do the Daytime running light's work ?

Check the front and rear turn signals on the left. If both are just as bright as the right turn signals, then the dim bulb is isolated just to the dash. Possibly someone replaced the bulb at one time with the wrong rated bulb. A steady dim bulb doesn't sound like a loose ground. It would probably be going in and out or flickering, and just that one side would not have a separate ground. High resistance in a wire (like broken strands)or a connection could cut the current and cause a dim bulb. If the whole left side is dim, both the dash and the signaling bulbs, start looking for high resistance in that side of the circuit. To thoroughly check it out, probably need a volt meter

Could have connection issues at the BCM - body control module , lose ground . The BCM controls all the thing's your have problems with .
Turn Signal Lamps
When the turn signal switch is place in either the right or left turn position, the turn/hazard request circuit is pulled low, through a resistor. The body control module (BCM) uses the resistors to determine if the left or right turn signals have been requested. The BCM then supplies an ON-OFF voltage to the turn signal lamps and turn signal indicator on the selected side of the vehicle. The turn signals receive a ground at G101, G401, or G403.

When the ignition switch is turned to the ON position, the vacuum fluorescent (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 IP dimmer switch. At the same time all vacuum fluorescent (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 instrument panel dimmer switch through the instrument panel dimming lamps control circuit. The setting of the instrument panel dimmer switch determines the amount of voltage that the instrument panel dimmer switch supplies to the BCM through the instrument panel dimming lamps low reference circuit. The BCM then sends a pulse width modulated (PWM) voltage to all the interior lamps. All the vacuum florescent (VF) and incandescent back lighting lamps are provided a specific voltage and are then grounded. When the headlight switch is turned to the PARK or HEADLAMP position, all incandescent back lighting turn on at the dimming level indicated by the IP dimmer switch. When the IP 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 IP dimmer switch.

Engine Coolant Indicator(s)
LOW COOLANT LEVEL
The IPC illuminates the low coolant warning indicator when any of the following occur:
• The BCM detects a low coolant level condition for at least 30 seconds. The IPC receives a class 2 message from the BCM requesting illumination.
• The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 3 seconds .

The thing to do first would be to hook up a factory or professional type scan tool an check for Instrument cluster or BCM DTC'S - diagnostic trouble codes . Then checking connection 's at the BCM , testing power an grounds .


ECM Inputs and Outputs Diagnosis

Open Circuit Detection Wiring Diagram 1

Replace the turn signal switch. All of these lights run threw it.

go here. we can help you. Also, did you check the headlamp relay in the box under the hood? One relay is in box in front of battery, other is in narrow box along passenger side fender under the hood. swap left & rt headlamp relays to see if it changes.

http://groups.yahoo.com/group/villagerquest/

Recheck the bulb number. This happens when the wrong bulb number is installed. Otherwise it could be a bad headlight ground.