Dimmed Backlit Dash and Radio/HVAC Lights

[EddieC]

I just replaced the Head/Fog Lamp switch (with oem) and all the functions work but the intermittent dim problem persists.
Is there a light sensor somewhere? I see a little dark half sphere far forward on the dash that may be it, but I hope not because it must be inaccessible from below.

 

[mikez71]

I removed my front panel to pop the sensor out..
definately not accessible from below or through the radio hole..

 

[EddieC]

I removed my front panel to pop the sensor out..
definately not accessible from below or through the radio hole..

Not my year but I watched a video on a 2006 and it was major surgery to get the dash top panel off.
Not possibly worth it just to chase dimmed dash reporting lights.

Revised: On closer investigation I see access is from the top by removing the forward strip of the dash. I have been advised that the windshield side pillar covers need to also come off to release the dash panel.

 

[mikez71]

It's not too bad, but you risk breaking some clips forsure..

Every morning lately the dash is dim. Bright enough for sunglasses (cloudy) but my dash is dark.
I will be happy to finally wire a switch, I'm just looking for a good 3 position dial ...

 

[EddieC]

It's not too bad, but you risk breaking some clips forsure..

Every morning lately the dash is dim. Bright enough for sunglasses (cloudy) but my dash is dark.
I will be happy to finally wire a switch, I'm just looking for a good 3 position dial ...

My Tahoe has a dial to adjust the gage and radio lights and I leave it fully bright (just below illuminate dome) but when the system dims it's not bright enough.

Now for a "DUH" moment. I ran across a video showing where a fellow cleaned the little ambient light sensor nipple and it affected his DRL to headlight function. Worth a shot.

 

[EddieC]

I removed my front panel to pop the sensor out..
definately not accessible from below or through the radio hole..

How does that get done?
I suspect mine because the headlight switch is set to automatic but the lights are on in the day.

Revised to note that the procedure is now apparent.

 

[mikez71]

If I remember right, you remove the a pillar trims.
1 screw up top (phillips or 7mm?), grab handle bolts on passenger side (10mm? after prying the covers off)
Then there are 5 or 6 clips along the edge facing you, so you just have to pry it up..
OF COURSE you risk breaking the tabs on the defroster panel that hold the clips, and the little plastic receptacle holes underneath.

I'm planning to add a parallel resistor to ground to reduce the sensitivity to darkness. (as well as a switch to manually select dim/auto/bright)
Lately it's been dim every morning despite being plenty bright outside.

I bought an adjustable resistor to help me pinpoint the resistance value that I need.
Will post details if I ever get to it.. You bringing this up has got me thinking about getting on it!

 

[mikez71]

7 total clips hold the defroster panel on. 3 on each end ~6" apart. 1 in the middle.
Picture below is of the two right most clips.


The backlighting changes modes with key on accordingly:
from dim to day once resistance drops below 3.14k ohm
from day to dim once resistance rises above 4.92k ohm

The values were measured by manually twisting a variable resistor before repeated keyon/keyoff cycles.
Once the adjustment caused a change in backlight with key-on, I would remove the resistor and measure it.
I should be within a couple hundred ohms or so..

So between 3k and 5k, key-on appears to default to the previous shutdown mode.
(Only tested with repeating key-on/key-off cycles, not shutting down for any length of time)

With the engine running, if I adjust the resistance in real-time near the 3k or 5k switch points, it can take several seconds to change. (~15 seconds or more.)
But if the resistance is low or high enough (my resistor was a 0-10k ohm variable), it will still take 2-3 seconds to change mode.

Installed a 10k resistor on the backside of the light sensor plug parallel with the sensor.
At dusk, the backlight was still dim. Hopefully it will be bright in the mornings, otherwise I may go back to my parking light activated relay.

 

[EddieC]

Ok, to close out the issue; Changing the ambient light sensor in the front dash panel cured the erratic dimming instrument/radio and hvac lights. I will mention that I previously changed the headlight/dimmer/4wd switch panel and it did not change the issue so others might do well to start with the light sensor.

Changing the sensor is not difficult but mine took more time than it should have after I dropped the old sensor down into the defroster duct! That added about 45 minutes working with a flashlight shining into a mirror and long slinky cable pickup tool to flip the sensor around so it was in the right position to be grabbed and pulled out. The whole process gave me a new respect for my dentist's talents.