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Dash Lighting Dim, Low Voltage

7K views 42 replies 5 participants last post by  GOPHERIT 
#1 ·
I have an interesting bug I think and Im not sure where I went wrong. A little background, I was using the interior lighting circuit from the headlight switch (pink wire I believe) that was variable voltage that went to the inverter to light my 3 pod gauges. This was great until I realized that I couldn't dim the gauges with the variable voltage line, and I needed a constant 12+ source.

Well, I waited to long to fix it and I believe I killed the inverter on the gauges, not a huge deal. Well when that happened, the other interior lights on the dash (steering wheel, headlight controls, butt warmer...etc) were VERY dim, almost to the point where you couldn't see them, even at night. Well just today I went in and disconnected the wire that was feeding the broken inverter, expecting to get full brightness again. Well, they did get somewhat brighter, but even at full bore, still not super bright. The circuit seems to be about 4V DC.

My question is this. What is the normal voltage on the variable voltage interior lighting circuit and does 4V max seem too low. If so, any thoughts on where I would begin to find the issue?

Thank you!
 
#3 ·
Correct, its actually strange you asked that because for the last two presses of the button to increase brightness, the lighting actually gets much dimmer (with the exception of the gauge cluster which still gets brighter) But yes, I have it to the "brightest" setting.
 
#4 ·
I tried some random testing of the background lights. Man is it easy for me to get completely confused as to what does an does not happen. If I haven't opened the drivers door for about 10 minutes, all the red lights *will* come on once I open that drivers door. If I try doing that any sooner than giving that car about that 10 min reset period, those red lights will not come on upon opening up the door. On the engineering page, I read 4.3 volts DC. Not sure if that value changes when the engine is running with the higher B+ voltage supplied by the Alternator powering up the systems. All the red background lights look balanced in my car. I think I saw that the background lights are divided up into 2 groups, and powered by 2 separate circuits from the BCM. If that is correct, maybe I can figure out which ones are grouped together. But if all your red as well as your gauges in the IP cluster are having illumination problems, it might have become a BCM type of problem.
 
#5 ·
So my custom 3 pod gauges are a separate issue not to be confused with the rest of the interior lights issue. I was curious where the voltage was being controlled, I wasn't sure if it was actually controlled in the headlight dimmer switch itself. That would be easy enough to replace. Ill have to take a look at the engineering page as well, great call. I would be surprised if they were separated into two separate circuits. I suppose while it is possible, they all seem to just be red low voltage LED's actually on the boards themselves. I don't know why I was surprised to learn that the illumination circuit isn't 12V, I guess it wouldn't make any sense to do the voltage reduction at each individual board (steering wheel, HAVC, headlight, butt warmers...etc). Really should have know better when I hooked up the background dial illumination for my gauges. Im not even sure I checked what the voltage was.... No wonder I ruined the inverter running off like 4Vs
 
#6 ·
I read 4.3V on the switch voltage as well, not sure that tells me much. Does the shifter have lights btw? On a related note though, if/when I figure out where my issue is, I still need to find a constant 12V+ source that comes on when the lights are on to correctly power my gauge backlights. Thoughts?
 
#7 ·
Anything 4.3 volts is power for sensors/computer. Stay away from it. All lighting is 12 volt.
 
#8 ·
So that circuit should actually be a 12V circuit? Or is it a low voltage control circuit and the LEDs are taking power directly from the board themselves? Just interested to hear that might be a 12V circuit, doesnt even seem close, only having between 2-4 volts depending on dim level.
 
#9 ·
Since I've never had to mess with the background lights, I'm also learning that the background lights are supplied with approximately a 12 volt signal to illuminate (when at full bright). You could lift out your multi-function panel from the center console, and using a multimeter, place the leads across the X1 connector pin 1 yellow wire (background lights power) to pin 2, black ground return wire to see what voltage shows up going from max bright to max dim. If you feel that the window/door control module still has good/proper background light illumination, you could then test that module doing the same thing with the meter. That's connector X2 pin 11 yellow wire (background lights power) to pin 4 black wire (ground return).
 
#10 ·
When you say "multifunction panel" are you referring to the stereo HVAC unit in total? If so, which is the X1 connector? That signal is coming from the BCM to that unit then?
 
#12 ·
So that is very interesting and I'm glad you mentioned it. My mother spilled her oatmeal (very runny) all over the center console and damaged the window switch and locks and had to be replaced. The multi function module was also affected and one of the butt warmer lights (high setting) no longer lights but everything still functions properly. Any chance this may be causing my issue?
 
#13 ·
^^^^^ I would think that if you lifted that module up an out, disconnect the connectors an power up, you should be able to see the results. That module *might* be causing a voltage drag on the circuit. Coarse, If it solves your problem, you'll have to spend a few more bucks for a fix.
 
#14 ·
The variable switch has multiple resisters in it. When you change intensity, there is a positive wire needle that moves along the resisters. The more resisters the power goes through, the dimmer it gets. A many years ago dimmer switches would actually catch on fire or melt due to people driving with very dim lights. Dim lights = high resistance. High resistance = heat. Obviously this issue is controlled in present time. I haven't looked at our switch, but I think ours has the resisters in it. Some of the new cars I have seen the switch is only a command send to the BCM. And the BCM regulates the voltage going out.
 
#15 ·
Very interesting point. Are those resistors or and the voltage drop actually coming from that butt warmer module itself?

Next time I'm in the car I'll bull the module and post back my results. I never would have thought could have been an issue.
 
#19 ·
That is the only unit that wasn't replaced. The window control switch was replaced. Correct if if I'm wrong, does the shifter have lighting as well? I honestly can't remember and if it does/is supposed to, mine is completely out. I'm still hoping that is they're all on the same circuit and that for whatever reason that module is lowering the overall voltage due to the moisture damage. Ordered a new heated seat switch today, just to rule it out.
 
#20 ·
The shifter does indeed have integral lighting. That display is in white. From memory, I'm pretty sure there are 2 tiny replaceable lamps under that trim plate, if R&R is ever required.


Come to think of it----- Since the modules fore an aft of the shifter took a oatmeal hit, maybe the shifter area joined in on the party (illumination wise).
 
#21 ·
Haha I may have a few issues... My mother is becoming infamous by the sound of it. Is there an interested board for the shifter lights as well then or just a harness with some lamps?
 
#22 ·
They do have a short wire harness assembly you could replace if needed. It carries an astounding price tag of about $135 (92202309). So you best hope its OK. Even the lamps are excessively over priced at about $ 14 each (92191396). Worth at least a try at refurbishing all 3 components, prior to possibly having to buy any of them (at least in my opinion).
 
#23 ·
Don't just go blowing money replacing parts. If the lights are out I think you might have a short to ground somewhere or a wire is broken. Have you been able to trail any of the wires to make sure there is no damage?
 
#24 ·
I'll take apart the whole dash when I get back. I need to anyway to fix the illumination properly for the gauges. Anyway, any more thoughts as to where I could find a 12v constant power source to run the gauge backlighting off of? I shouldn't be running that of the variable voltage illumination circuit anyhow as the inverter for the gauge backlighting didn't seem to care much for that.
 
#25 ·
I've lost track of the existing condition of those background lights, as it stands now. You are saying that you still have most (if not all lights) still acting up, even with all 3 back lighted items on the lower console disconnected ?



If you were using PK/D-BU (pin 10) wire at the headlights control switch, it does say that wire is an *ignition on* 12 volt source. If its for integral lighting of those gauges, I'd think that is the wire to use. Don't think you would be trying to find a (constant power) B+ source for them.
 
#26 ·
Currently, the custom speed hut gauges illumination has been completely disconnected from the illumination circuit. All lighting (steering wheel, heading switch, window switches, etc) are very dim and are only at about 4 volts at max brightness. The shifters have no lights currently, so I still need to look into that. Currently I'm on vacation through the rest of the week but I may have a chance on Sunday to start pulling modules one at a time. Sounds like I may have a few issues. First going to disconnect the seat heater and see where that gets me. Also going to look into the shifter illumination for existing water damage and see what kind of voltage I'm getting even if the lamps are burnt out.
 
#28 ·
Is that just a switched 12v source? While I suppose that would work, really looking for a 12v non dimming illumination source if at all possible!
 
#29 ·
Is that a ignition switched 12v voltage source? While I could make that work, I would really like to look for a non dimming 12v source that's only on when the rest of the illumination is on. If I can't find one, I'll need to use a relay and use the dimmed illumination circuit to control a 12v switched voltage source.
 
#30 ·
Alright so quick update. Pulled apart the whole shifter today and got a decent look at everything. Removed the butt warmer module and no difference. I have no light at all in either of the two LEDs in the shifter. I don't have my multimeter here but I'm betting I'm not getting any voltage if both lights are out. I did have one thing that made me think... What is the purpose of this small board? Looks like it has a few separate resistors, curious what it's purpose was. Any idea why I wouldn't be getting voltage to these lamps? Vehicle Auto part Car Engine City car
 
#31 ·
Ah, ignore my question about the board. Realized its the manual shift controller.
 
#32 ·
So I really got into things today. Turns out the shifter LED lamps work fine when attached to a 12V battery, so no issues there. The entire illumination circuit (tested at those small shifter lamps and headlight switch) only reads a maximum of 4.7V. That is why the lamps are dim and the shifter lamps are not even hitting the threshold voltage for the LED to illuminate, thats why the look out completely. Now that I know why I am having the issue, I need to drill down why I am not seeing the full voltage of around 12V max for this circuit. Now it sounded like this circuit is receiving power from the BCM, can anyone confirm this? If so, can I verify at the source it is only outputting 4.7V max when there is no load? I want to confirm the wiring and lighting are all correct and that the voltage source is low. Any more thoughts are greatly appreciated.
 
#33 · (Edited)
For the life of me, I can't find any information indicating that the background lighting would/should be seeing 12 volts when at the max light level. As a side thought, if all the cars came wired up, an function the same way to an thru the BCM, you can test these things. With my car sitting in the garage an ignition on, (an dark enough to require the headlights to turn on), I can see these things happening. First I rotated the light switch to the parking lights position (to lessen the drain on the battery), A/C switched to off (to shutdown the cabin fan), radio left on to see what the screen might want to do.
#1---- Cycling the headlight switch to the stealth mode,*only the DIC an radio screen* remain illuminated (switch then returned to parking lights position). #2----Using the min/max dimming switches, I cycled them to the stealth mode. Only the analog speedo, tach and DIC remain illuminated. Then cycled back to the normal mode. #3---- Using the dimmer switches, min or max direction, causes *all* background lighting to follow (except that the radio screen appeared to have very little change, which is OK by me). It also appears that the radio,HVAC control module, instrument cluster, and the DIC, lighting are controlled on a digital data bus line signal for illumination commands. Maybe somebody (who has been following along) has 1 or more of the 3 components currently loose/disconnected on the console, and can perform a check of the min/max background lighting voltage output found. This way we can be sure of the voltage range used on that lighting circuit.


If all your red lights are dim, can you tell if all 4 instrument cluster gauges (that use white background lighting), are also dim ?





Added thoughts------- Whether you press the brighter or dimmer switch (on the lights control module), you are only creating a ground potential. So those press switches are causing a BCM rheostat type of action (like electronically increasing or lowering the circuit resistance) to adjust the background light illumination level. If you can obviously see a change going up or down in the lamp illumination level, I doubt either of those 2 switches could be the problem. But if you want to sorta override the circuit a touch , you could jump some pins to see if any change happens. With the connector removed, jump pin 7 (GY/WH) to pin 4 (BK), to force the background lights to go full dim. Then jump pin 12 (GY/D-BU) to pin 4, to force the lights to go full bright. There's always that chance that your bright/max switch has a problem, if the dim side seems to work correctly.
 
#35 ·
For the life of me, I can't find any information indicating that the background lighting would/should be seeing 12 volts when at the max light level.

My thoughts at first as well, I just thought maybe it was a 2-5V circuit since they were all LED's and I read on a previous post on another thread that may be the case. Now I am 85% sure it is a 12v Circuit because the inverter worked for a time and I assume it wouldn't work at ~4V and the shifter lights say +12V right on them

As a side thought, if all the cars came wired up, an function the same way to an thru the BCM, you can test these things. With my car sitting in the garage an ignition on, (an dark enough to require the headlights to turn on), I can see these things happening. First I rotated the light switch to the parking lights position (to lessen the drain on the battery), A/C switched to off (to shutdown the cabin fan), radio left on to see what the screen might want to do.
#1---- Cycling the headlight switch to the stealth mode,*only the DIC an radio screen* remain illuminated (switch then returned to parking lights position). #2----Using the min/max dimming switches, I cycled them to the stealth mode. Only the analog speedo, tach and DIC remain illuminated. Then cycled back to the normal mode. #3---- Using the dimmer switches, min or max direction, causes *all* background lighting to follow (except that the radio screen appeared to have very little change, which is OK by me). It also appears that the radio,HVAC control module, instrument cluster, and the DIC, lighting are controlled on a digital data bus line signal for illumination commands.

With headlamps turned to the "On" position, all lamps except for the HAVC/Stereo and instrument cluster are dim.

Maybe somebody (who has been following along) has 1 or more of the 3 components currently loose/disconnected on the console, and can perform a check of the min/max background lighting voltage output found. This way we can be sure of the voltage range used on that lighting circuit.

This would be useful but I am fairly sure at this point its a variable 12V circuit

If all your red lights are dim, can you tell if all 4 instrument cluster gauges (that use white background lighting), are also dim ?

No issues at all here or on the HVAC/Stereo, full brightness

Added thoughts------- Whether you press the brighter or dimmer switch (on the lights control module), you are only creating a ground potential. So those press switches are causing a BCM rheostat type of action (like electronically increasing or lowering the circuit resistance) to adjust the background light illumination level. If you can obviously see a change going up or down in the lamp illumination level, I doubt either of those 2 switches could be the problem. But if you want to sorta override the circuit a touch , you could jump some pins to see if any change happens. With the connector removed, jump pin 7 (GY/WH) to pin 4 (BK), to force the background lights to go full dim. Then jump pin 12 (GY/D-BU) to pin 4, to force the lights to go full bright. There's always that chance that your bright/max switch has a problem, if the dim side seems to work correctly.

While its worth a try, are we sure this is safe for the circuit? Last thing I want to do is fry the BCM or the whole illumination curuit
The items controlled by one of the BCM dimming circuits is, transmission shift position lights, TC and seat heat module, door lock/window control module, steering wheel controls, headlight control module, and the dome light control light push buttons. The cars were/are supposed to include 2 white 3 pin connectors stowed at the proper locations, that *could* be activated if you were to add/convert to the fore and aft cigar lighter capability. Each one of those connectors has a wire included in their wire looms for powering up a light, that would allow (the cigar lighter fixture) to be dim/bright controlled by the same circuit that controls the above. Then again, that would give you another source for powering up any added gauges (for instance), as long as that power available, actually goes from near zero to 12 volts (if that turns out to be what this circuit supplies).
The more and more we discuss this it sounds like there isn't a factory 12V on or off for the illumination, just the dimmer line. I remember back in the day installing aftermarket stereos into cars and they always asked for both of those lines but they were separate wires on the factory loom. I suppose the G8 simply controls all that via the BCM and has no need for the 12V on/off wire. That being said, I can simply use a transistor or a small relay to control an ignition switched 12V line to supply background gauge power, shouldn't be too hard and I'm not too worried about it.
Really just want to figure out why I am not getting the 12V I should see on the circuit and if there is a way to test. Would really like to find where the voltage originates (BCM) so I can remove all the lighting (unplug) and just see what voltage the BCM is outputting. Have to start to narrow down what could be causing the issue.
 
#34 ·
The items controlled by one of the BCM dimming circuits is, transmission shift position lights, TC and seat heat module, door lock/window control module, steering wheel controls, headlight control module, and the dome light control light push buttons. The cars were/are supposed to include 2 white 3 pin connectors stowed at the proper locations, that *could* be activated if you were to add/convert to the fore and aft cigar lighter capability. Each one of those connectors has a wire included in their wire looms for powering up a light, that would allow (the cigar lighter fixture) to be dim/bright controlled by the same circuit that controls the above. Then again, that would give you another source for powering up any added gauges (for instance), as long as that power available, actually goes from near zero to 12 volts (if that turns out to be what this circuit supplies).
 
#36 ·
This is all I see that can do if you want to go that way >>>>> 4 of the 6 module/items that are powered up by that dimming circuit, are hard wired from the BCM (no intermediate connectors to isolate them). IF you were to remove the connector from the BCM to see what power is coming out of it, I don't know if it would even show any power. There are so many important circuits that would be cut off (by disconnecting same). The best you could do (in my opinion) is to locate that wire (a little downstream from the connector itself). Then cut that wire that powers up that dimming circuit. That would allow all the other circuits to continue to operate normally while checking the output voltage . The connector is X3 (blue in color) The wire is pin 18 (yellow in color). After checking as needed, you could then re-splice that wire.
 
#37 ·
This is all I see that can do if you want to go that way >>>>> 4 of the 6 module/items that are power up by that dimming circuit, are hard wired from the BCM (no intermediate connectors to isolate them). IF you were to remove the connector from the BCM to see what power is coming out of it, I don't know if it would even show any power. There are so many important circuits that would be cut off (by disconnecting same). The best you could do (in my opinion) is to locate that wire (a little downstream from the connector itself). Then cut that wire that powers up that dimming circuit. That would allow all the other circuits to continue to operate normally while checking the output voltage . The connector is X3 (blue in color) The wire is pin 18 (yellow in color). After checking as needed, you could then re-splice that wire.

Great information. As much as I hate to do it, I think you might be right in how to test. Curious to see what happens... Almost thinking that it's a wiring/ grounding issue since I still have the dimming control (albeit low voltage) which tells me the BCM is still taking in signals and modulating the voltage. I'll report back next time I'm in front of the car.
 
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