Dim Map/Reading Lights

[gpking]

I've seen this issue complained about a bit online but I was never able to find a solution for my specific truck.
Anyway, having an '03, I have the horrendous dome/map lights that don't put out any light. I swapped all the bulbs to LED and the dome lights are bright enough to read by, the only problem is the map/reading lights are still completely worthless.
I assumed the button for each of my map lights were just defective (they don't work every time and strobe the bulb sometimes) so I installed an Envoy dome light in place of one of my broken originals, but it is worthless too.
This leads me to believe the map lights aren't getting enough power, and the buttons are junk. Not enough power being the main cause of the problem.

I looked at the wiring diagrams in the appropriate service manual, and the map lights are powered off of pin B18 on the BCM- separate from the power for the dome lights.
I haven't ripped anything apart yet to test, but my guess is it isn't feeding them 12v.

Other owners online have claimed opening and shutting the lighted visor mirror brings the map lights to full brightness temporarily. I can't confirm this because my visors don't have lights.

I started this thread mainly to remind myself to try and find a solution this weekend, but also to see if anyone else has managed to fix their map lights permanently.

 

[Mooseman]

Yep, I have the same issue if only turning on the reading light. Only solution I've found was to open the vanity mirror. I don't know why, it just works. They must be wired together or something.

When opening the door though, it's full bright.

 

[Blckshdw]

I'm not too sure about the non functioning button thing you've got going on, but the reading lights vs dome lights brightness is a platform wide issue. I suspect they are on a PWM signal, same thing as DRLs vs low beams. If you pulled one of the dome lights down, you probably noticed there are 3 wires instead of just a positive and negative.

 

[gpking]

Correct, the dome lights and vanity mirrors are wired together. Looking at the schematic, I'm not sure why they make any difference. The only problem is I don't have lighted vanity mirrors.



To clarify, all lights come on full brightness as dome lights, but if I trigger the map light, the map light will go to like 50% brightness. Off, and it returns to 100% again.

The solution I had thunk up would be to cut B18, then fuse it and run the end that goes to the map lights directly to a power source. I'll need to get the multimeter out and see if B18 really is the problem though before I try this.
All I know is I've chased the issue all the way to the BCM.

 

[DAlastDON]

I read your post last night and did some research myself. Could not post because my cable service went out.

The courtesy function of the overhead console light is PWM controlled. The map light function is not. I went out to the truck last night and observed the overhead console lights. All doors closed, lock or unlock the doors and the lights are slightly flickering. But if you enable the map light function of the light the flicker stops and the light gets slightly brighter.

The map function and vanity mirrors do run off the same power source. Battery Rundown/Inadvertent Power. Its active for 20 minutes after the key is turned off. Possible retained accessory power if you don't go with one of the modules for chimes and on*.

Screen shot these for ya.

 

[Blckshdw]

Good thing we all know how to do the capacitor mod

 

[DAlastDON]

Good thing we all know how to do the capacitor mod

True. Wouldn't even interfere with the dimming of the lights when they go out.

 

[gpking]

I read your post last night and did some research myself. Could not post because my cable service went out.

The courtesy function of the overhead console light is PWM controlled. The map light function is not. I went out to the truck last night and observed the overhead console lights. All doors closed, lock or unlock the doors and the lights are slightly flickering. But if you enable the map light function of the light the flicker stops and the light gets slightly brighter.

The map function and vanity mirrors do run off the same power source. Battery Rundown/Inadvertent Power. Its active for 20 minutes after the key is turned off. Possible retained accessory power if you don't go with one of the modules for chimes and on*.

Screen shot these for ya.

I have a 2003 so I have no console lights (I want to upgrade though). I've never been in a 2005+ Trailblazer/Envoy/etc so I don't know if the map lights are defective too. I know the 2002-2004 buttons are absolute junk though, which only contributes to making the map lights worthless.
I assume you took that screenshot from the '05+ Service Manual since it's different from my screenshot from the 2004 Service Manual (before the redesign).
Can any '05+ owners confirm their map lights work at more than 50% brightness? If so GM likely fixed the issue.

The weekend is creeping closer and then I'll be able to tear some stuff apart and see what the problem GM couldn't fix for 3 years is.

 

[djthumper]

I have an 06 and they are dim so they did not fix the issue.

 

[DAlastDON]

I also still have the incondesent bulbs in. No LED's yet. I could see the PWM being noticed more on LED's though.

I have a 2003 so I have no console lights (I want to upgrade though). I've never been in a 2005+ Trailblazer/Envoy/etc so I don't know if the map lights are defective too. I know the 2002-2004 buttons are absolute junk though, which only contributes to making the map lights worthless.
I assume you took that screenshot from the '05+ Service Manual since it's different from my screenshot from the 2004 Service Manual (before the redesign).
Can any '05 owners confirm their map lights work at more than 50% brightness? If so GM likely fixed the issue.

The weekend is creeping closer and then I'll be able to tear some stuff apart and see what the problem GM couldn't fix for 3 years is.

Correct. 2008 FSM.

 

[gpking]

Interesting. It seems odd to me that something like this wouldn't get fixed in the redesign.
I know GM doesn't test anything before it rolls out, but this is rediculous.

While I'm at it, I think I might throw some footwell lights in too so I can see everything.

 

[gpking]

I got a little motivation and hooked the multimeter up to each of the three prongs on the dome lights (the driver's one) and actually think this might not be a problem that can be fixed... easily.
The gray wire (courtesy lights) supplied 12.5V when a door was open or they were manually switched.
When a door closed, however, it would fade from 12.5V to 0V, then almost instantaneously pop up to 2.5V. This intrigued me because I noticed after I installed LEDs this winter, the cargo light glows very dimly almost all of the time, perhaps due to the 2.5V.
The orange wire (map lights) supplied 12.5V constantly, which is what it is supposed to do.
The black wire (negative/ground) obviously read 0V.

What concerns me is the 2.5V on the gray wire. If the map lights were grounded on their own to a true 0V source, they would be supplied with 12.5V since that is the difference in voltage (12.5 - 0 = 12.5).
But since the map lights are tied in with the courtesy lights, supplying 2.5V, the map lights are only getting 10V (12.5 - 2.5 = 10).
Forgive me if this is incorrect, I'm no electronics expert.

 

[Mooseman]

It's not a design flaw if it works with incandescent bulbs like it was designed to. We are the ones modifying it. Just like when putting in LED's for turn signals and getting the hyperflash and the side markers not working right.

 

[gpking]

The reason I did LEDs was because the map lights weren't bright like they should be. This problem has existed all throughout history in my experience with TBs. My neighbors owned a 2003 TB EXT years ago and it had the exact same issue mine has.

Yes, the problem with the cargo light dimly glowing was introduced by the LEDs, but the map lights have never worked like they should, even with the original bulbs.
Here's a video demo of what I am experiencing.
Notice how bright the courtesy light is compared to the map light.

[video]https://www.youtube.com/watch?v=fyK2qVZ8a88&feature=youtu.be[/video]

 

[IllogicTC]

If you're getting the same voltage no matter the wire, perhaps it is the design of the bulb itself. Wouldn't exactly explain LEDs doing the same thing, though, but it's just a thought. I haven't pulled one recently to tell if it has multiple filaments or not.

 

[Mooseman]

Then the only way to get out of it would be to separate the reading light from the courtesy and wired directly to 12V. Problems with that is you will lose the reading light as a courtesy (obviously) and the possibility of running down the battery if one is inadvertently left on. My kids have left some on and they do get turned off after a while. Or you wire it to a switched 12V.

I hadn't noticed it before because I hardly use the reading lights and I also went to LED's. Only noticed it after. My cargo light doesn't flicker neither.

 

[IllogicTC]

Checked mine in the dark, 05 TB, as far as I know it's either factory bulbs or direct replacements to them, and my map and courtesy lamps are the exact same brightness.

 

[Toiyabeshawn]

Hello all. I just wanted to add some info as to what I ran into with interior dome/map LED installation in my 2004 XUV. First off, I have purchased sooo many “garbage” low cost LED’s from eBay and other online sellers with very disappointing results. Do yourself a major favor, pay the price and buy quality name brand LED’s, it will be a big savings in the end, both time and money! I hate the influx of cheap, inferior chinka made crap! I have finally spent the money and went with Sylvania ZEVO LED’s ( mine were made in Italy) and I am impressed with the quality of the lamps and the real “lifetime” warranty that you only get with a quality name brand product. Anyhow, my Envoy XUV has the dual function dome/map lights over each seat. I installed the ZEVO 194 blue LED’s in the four “dome” lights at each seat and ZEVO 194 white LED’s in the four “map” lights at each seat as well as the two cargo area lights in the back. Well, all of the lights come on like normal, full brightness with the doors open or the dash light switch turned on. I have to say, I am pleased with the brightness of the LED’s and the blue/white combo at each fixture has a real cool effect, in the “dome” light function, with all blue and white lights on together, it’s just right for me, not too blue or too white, just right. Anyhow, The map lights (white) when turned on with their individual switches, are dim, less than 50% bright and useless! I checked the supply power on the leads to the lights, both circuits supplying the “dome/map” lights were getting 12.5+ volts, normal right? Well, when I replaced one of the “map” bulbs with a regular 194, the other three “map” lights with their LED’s still in, went to full bright! With the regular 194 removed, the other three LED maps would work full bright for a while the would go back to being very dim. I got to thinking that the full time 12.5 volt circuit feeding the “map only” function must be fed through a solid state circuit of some kind that requires the “load” current of a normal 194 incandescent bulb to overcome some kind of electronic glitch. I ended up soldering a 2 watt 160 ohm metal oxide film resistor across the brass socket tabs at each map light socket and BAM! Problem solved! The resistor adds just enough “dead load” about 1.4 watts, to fool the circuit into thinking that a regular 194 is in the socket thus making the LED’s bright like normal. BTW...an incandescent 194 lamp runs at 3.8 watts at 14.0 volts so the resistor fix uses less power overall. !!! A CAUTIONARY NOTE !!! IF you do this mod to your map lights, make sure you leave the resistor leads full length and tuck the resistor up and away from the plastic housing as this resistor will get quite warm, like the old 194 bulbs would but as long as you keep the resistor clear of the housing, you’ll be fine. //NOTE// the resistor is active in the circuit ONLY WHEN the map light is on..either with the door open/dash switch turned on OR if the individual map light switch is turned on.. There is plenty of room around the light housing to position the resistor! I will post my experience with installing ZEVO LED’s in my turn, tail, brake and side marker lights soon.. absolutely amazing how they look!😎

 

[Blckshdw]

@Toiyabeshawn any chance you could post some pics of the interior with the blue/white combo setup?

Thanks for finding a pretty easy fix for this issue, this should come in handy for future people who might run into it.

 

[Toiyabeshawn]

@Toiyabeshawn any chance you could post some pics of the interior with the blue/white combo setup?

Thanks for finding a pretty easy fix for this issue, this should come in handy for future people who might run into it.

I’ll get some pics tonight of the interior when it’s dark.. the blue/white combo looks pretty cool😎