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Discussion Starter · #1 ·
Hello everyone. Hope there are still some people lurking around that may have an answer to my odd headlight issue.

To start, I'll say that these are Ebay headlights housings. I put some LED bulbs in them from TheRetrofitSource. I never did the DRL kill mod. I've been having an issue where the passenger side low beam works every now and then. Lately though, it seems to be not coming on at all. A while back I swapped the passenger bulb to the driver side(while the pass wasn't working) and it worked fine on the driver side. I thought maybe then there was an issue with the housing, and got new Ebay housings(2nd set). It worked fine for a few days and then the issue started again. My next thought was maybe something with the LED bulb messing up. I picked up some halogen bulbs and tried both in the pack and neither works. I got out my multimeter and with the headlight switch on, I have 12v at one terminal of the plug for the bulb, the other shows continuity to a bolt in the engine bay, so I believe that means it also has a good ground. Anyone know why I would have 12v and a ground and the headlight wouldn't work?
 

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"works every now and then "

There's not much point in taking test results from one point in time and declaring a conclusion. You likely have a marginal wiring problem, to include a potential bulb socket issue.

The housings are irrelevant. EBay, not EBay. Old ones, new ones. They're just plastic boxes. The sockets and wiring are all on the vehicle, not on the housing.
 

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2004 chevy trailblazer_lt
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Go back to the original headlamp capsules. The LED bulbs do not draw enough current relative to the incandescent bulbs and the BCM (which controls the basic operation of the headlights) gets confused and the headlights do not work properly. Also the relay which is used to derive the DLRs from the low beam headlights won't work as designed. Actually it is not just a simple relay - it is an electronic switching module which turns on and off at a speed which presents an apparent lower voltage to the low beam light bulbs thus making them DRLs.

Also, the LED bulbs you purchased likely do not have the same light output pattern of the original bulbs to utilize the reflection optics of the lamp housing reflector and the resulting light pattern that comes out of the headlamp assemblies may not be properly focused/aligned on the roadway and could blind oncoming drivers.
 

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'05 Chevy TB EXT
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5,138 Posts
Go back to the original headlamp capsules. The LED bulbs do not draw enough current relative to the incandescent bulbs and the BCM (which controls the basic operation of the headlights) gets confused and the headlights do not work properly. Also the relay which is used to derive the DLRs from the low beam headlights won't work as designed. Actually it is not just a simple relay - it is an electronic switching module which turns on and off at a speed which presents an apparent lower voltage to the low beam light bulbs thus making them DRLs.

Also, the LED bulbs you purchased likely do not have the same light output pattern of the original bulbs to utilize the reflection optics of the lamp housing reflector and the resulting light pattern that comes out of the headlamp assemblies may not be properly focused/aligned on the roadway and could blind oncoming drivers.
Yup.
 

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2004 gmc envoy_slt_xuv
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Two years ago I bought a set of these LED bulbs on Amazon and replaced the cloudy housings. No problems whatsoever, and they are nice and bright.


Probably the best upgrade I've done to my XUV over the last 18 years that I've owned it.(y)
 

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Discussion Starter · #7 ·
"works every now and then "

There's not much point in taking test results from one point in time and declaring a conclusion. You likely have a marginal wiring problem, to include a potential bulb socket issue.

The housings are irrelevant. EBay, not EBay. Old ones, new ones. They're just plastic boxes. The sockets and wiring are all on the vehicle, not on the housing.
I mentioned the housings because some of the wiring does run through them. The main headlight plug with high and low beam wiring runs to a plug on the housing and then wiring from the other side of the plug runs inside the housing to the headlights. My thought was with them being ebay/china that maybe there was an issue with that internal wiring.

I didn't really declare a conclusion, I stated what was happening. Sometimes that headlight works just fine, other times it doesn't work.

Over this past weekend, I set out to do some more testing with it. The headlight was not working. I metered the headlight plug at the bulb and had 12v across it. I then plugged the LED bulb back in and saw that it was lighting, but with maybe 5% of it's normal power. I also tried 2 different halogen bulbs(that I have confirmed work) and got zero output. I tested the plug again to be sure and still showed 12v. I am not understanding how I can have 12v and not have light output. Could this be a grounding issue, even though I am showing a complete circuit with 12v at the plug?

Another thing I want to mention, is that these LED bulbs worked for 4 or 5 months before I started having the issue of the passenger side not working correctly. This isn't a fresh install having issues. For that reason, I don't believe it to be a BCM issue do to LED's drawing less current, but I could definitely be wrong as I've been wrong before.
 

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'05 Chevy TB EXT
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You cannot test a digital signal with a DVM ........ you need an oscilloscope - which I HIGHLY recommend that everyone own and learn to use ASAP!
A DVM cannot capture or cycle fast enough to actually "see" what's happening and you might see a spike at one moment and a dip at another and a null at a third point in time --- all that is a strawman result in that it does NOT represent the true voltage or digital duty cycle.​

Read on ....................................

ΘΘ --- you're being confused by several things about which you have made some bad and wild assumptions.

The bulbs - because they are "floating" (with no true ground nor a true + power, the least of which will be 12VDC or even 0VDC) and can receive different voltages by varying the grounds or the supply to make them behave in different ways - is not a test for a DVM.

Look at this pattern ...

Rectangle Parallel Font Pattern Number


This is only PART of what's going on .... the DUTY CYCLE is created by the time the voltage is up to a certain point in time and it then will drop to zero volts as the signal is shut off ...... unless the ground is really -6VDC and the power is +6VDC --- and that's a big fat ZERO VOLTS.

But --- there's another fly in the ointment ---> as I stated in the ZERO VDC line above ---- the ZERO VOLTS can be achieved at +/-12VDC or any point in between as long as the ground is the same-but-opposite for unity voltage gain.

Get it?

We used to call this: "Cascading Voltage" in that if we floor a transistor at the maximum output of the transistor before it, and the voltage output of the 2nd transistor acts as the floor voltage for the next transistor --- and if you keep flooring the next transistor with the output voltage of the last transistor --- theoretically the transistors don't really care --- until they blow out and self destruct.

Here's a sample of a cascading voltage generator .... notice all the transistors, one after the last and before the next --- they keep on jacking each other up, higher and higher voltage until the side of one of them blows out or the germanium melts.... whichever .......

Rectangle Slope Font Symmetry Parallel



That's how we get to operate the same bulbs in the same sockets with the same wires - only feed them different voltages by either varying the cyclic time/duty cycle-event and/or floor the bulb at a higher or lower voltage while the + side of the bulb is held to 12VDC --- well --- as you can see ---> we can vary the brightness by changing the --- (follow me here).

1. The (-) ground changes against a constant (+) 12 VDC voltage ........... OR​
2. the TIME/Duty Cycle changes and the voltage can stay at 0VCD on the ground and +12VDC on the power, but the bulb is only ON for a smaller percentage of the time as dictated by the "time/amplitude-ON signal" ............. OR​
3 We can assign both a TIME/DUTY CYCLE -- AND either a floored voltage verses a line voltage to illuminate the bulb.​
Now --- so far, I've only spoken of filamentous bulbs (the ones with the little wires in them) - NOT LEDs, which changes a lot of operational parameters.

FTR ---> LEDs MUST have a voltage differential as required to force luminescence by a different voltage (not so much a duty cycle) applied to their two contacts. Digital pulses CAN excite an LED - but the floor voltage has to be 0VDC or lower for the full 12VDC to get them to their highest production of light at the correct Kelvin range.

That we can "fool" the BCM or whatever 'x'CM is involved, with just a 30Watt resistor-to-ground ... makes it kinda easy for me to get operational LEDs in all my lighting locations. You might be fortunate enough if you go back to "simple" and start all over again.

It worked for me - accidentally or not ..................

......... just sayin' ...........................​
 
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