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Old 09-12-2022, 06:29 PM
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LED Taillights Problem

Hello everyone!


I just got my baby back and have ventured into putting in a set of LED taillights. I purchased them used off eBay so I'm not sure what brand they are, and I seem to have run into an issue, and they are not working as they should, and I'm hoping it will be a simple switch in the plugs to correct the problem.


When i turn the taillights on, the bottom most light, which is supposed to be the brake light, fully illuminates and stays on, and when i hit the brake, the top led section lights up, which is backwards. It should be the upper light being on when the taillights are on, and the bottom should also light up when i hit the brakes. My 2001 X5 has a 6pin connector, with only the middle 4 connectors being used, while the LED taillight connector has 5 wires, one is piggybacked to the first pin and isnt being used. I have attached pictures, and am wondering if i simply need to swap the correct wires in the oem connector to make these work correctly. Any help would be much appreciated.
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Old 09-12-2022, 11:15 PM
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So i ended up fixing the problem, I believe, but i think i'm missing something. simply by swapping the #2 and #4 wire on the oem harness, The top one now lights up as the taillight, and when i hit the brake, the bottom one lights up nice and bright. My question is should the bottom one be on as a taiillight as well, but get brighter when i hit the brake? or is this configuration correct? I have bmw scanner and am going to code out the cold check for the taillights and the brake lights.
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Old 09-13-2022, 04:31 PM
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Pre-LCI and LCI tails work differently so don't read much into what other examples of e53 X5 cars do - what did your original tails do?
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Old 09-13-2022, 05:10 PM
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Quote:
Originally Posted by wpoll View Post
Pre-LCI and LCI tails work differently so don't read much into what other examples of e53 X5 cars do - what did your original tails do?

I honestly don't remember what they did, I suppose i could switch back the 2 pins and plug in my old light to tell you, but i think i'm satisfied with the result, and i think i discovered why the brake light is not acting as a tail light.



I got my BMW scanner hooked up to disable the cold check for the brake lights and taillights. Interestingly, the error that shows up in the scanner shows it to be for the "rear side lights" and not rear taillights, and for the brake light. I took a look at the coding, and it shows that there is a section for Cold checks, but doesn't include an option for side lights or brake lights, but there is in the BC messages section. So i deselected the rear side lights and brake lights, and now i don't get any more errors. There was also an option called "brake lights as side lights", which was not selected. I imagine if i enabled that option, the brake light would then become active as a taillight, but i'm not sure since i switched the pins what effect that would have, guess i can just test to see, but also don't wanna bork things up and possibly fry lights.


Also noticing that the upper led taillight has a slightly noticeable flicker, i imagine this would be solved using capacitors like i've seen so many other people suggesting.
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Old 09-13-2022, 05:17 PM
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It won't fry the lights but it may not work either. The system is designed to work with incandescent lamps and not LEDs. To use a brake light as a tail light requires the LCM to modulate the voltage going to the brake lamps, in effect running it a lower voltage, simulating a lower wattage lamps (21W vs 5W). Modulating the voltage on the LEDS won't dim them - it will simply make them flicker.
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Old 09-13-2022, 05:34 PM
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LED's can be dimmed (of course not below the diode threshold voltage) but the voltage should be stable, not pulsing PWM like from LCM. Some capacitors might do the trick.
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Old 09-13-2022, 05:43 PM
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Originally Posted by Clavurion View Post
LED's can be dimmed (of course not below the diode threshold voltage) but the voltage should be stable, not pulsing PWM like from LCM. Some capacitors might do the trick.
I'm trying to keep my electrical explanations "conversational" rather than go full-on "electrical engineer" on everyone!

But yes, of course.

While caps would "average" or smooth the PWM pulses, reducing the forward voltage on an LED doesn't produce a brightness variation in the same way as would occur with an incandescent lamp, so the system would need to be reconfigured to give good tail and brake values.

Which I think can be done via BMW Scanner but I'm not familiar with what PWM values result in good brightness levels for LEDs.

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Old 09-13-2022, 05:50 PM
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Quote:
Originally Posted by wpoll View Post
It won't fry the lights but it may not work either. The system is designed to work with incandescent lamps and not LEDs. To use a brake light as a tail light requires the LCM to modulate the voltage going to the brake lamps, in effect running it a lower voltage, simulating a lower wattage lamps (21W vs 5W). Modulating the voltage on the LEDS won't dim them - it will simply make them flicker.

Gotcha, I will do some more investigating and see what happens when i enable that option. I imagine what will happen is the lower light will be illuminated along with the upper one as a taillight, but they're going to flicker, which means i need to put capacitors to eliminate it.
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Old 09-13-2022, 05:53 PM
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Quote:
Originally Posted by wpoll View Post
I'm trying to keep my electrical explanations "conversational" rather than go full-on "electrical engineer" on everyone!

But yes, of course.

While caps would "average" or smooth the PWM pulses, reducing the forward voltage on an LED doesn't produce a brightness variation in the same way as would occur with an incandescent lamp, so the system would need to be reconfigured to give good tail and brake values.

Which I think can be done via BMW Scanner but I'm not familiar with what PWM values result in good brightness levels for LEDs.


Just curious, why does your light coding page look different than mine? Is this a difference in the BMW scanner software, or difference per model of X5.
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Old 09-13-2022, 05:57 PM
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Originally Posted by chasers36 View Post
Just curious, why does your light coding page look different than mine? Is this a difference in the BMW scanner software, or difference per model of X5.
Not my image - borrowed it from another another BMW forum.

But if I recall correctly, yes, mine does look like this. It may be LCI specific - since the LCI makes MUCH more use of PWN in the lighting systems.

And in fact, LCI cars already use the brake lights as tails - from the factory. In fact, they don't even have any 5w tail lamps at all - they only use single filament 21W lamps in all positions in the rear, modulating them to be either tails or brakes as required.
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