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Ford Mondeo MK4 2008: LED H7 Canbus Bulbs Fading & Damaging Rapidly in Torsional Lenses

iDest 13347 18
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Why does a left H7 LED bulb in a Ford Mondeo MK4 fade and fail after a few minutes, and how can I prevent it?

The left-side LED is likely being stressed by the car’s lighting control and wiring: the cornering light is PWM-controlled, so the bulb is not getting constant voltage, and LEDs are a poor match for this kind of driver control [#16940708][#16940674] If the same good LED fails only on the left side, the car is at fault; if it survives there, the bulb itself is poor quality [#16940780] One reply specifically points to a corroded ground connection in the left lamp as the likely fault [#16941207] A suggested workaround was to add a 4700 µF, 35 V capacitor in parallel with the bulb supply to smooth the power [#16940674][#16940696], but that does not fix the underlying PWM issue [#16940708] Another note was that the car can be around 14.4 V while a battery is 12 V, which can push marginal LED drivers past their safe range [#16940780]
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  • #1 16939027
    iDest
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    Ford mondeo mk4, 2008. H7 headlights in torsional lenses, plus cornering lights.
    I replaced the classic H7 bulbs with LED H7 canbus. The right LED lights up correctly.

    There are problems with the left one. The cornering light turns on gradually and slowly - the more the cornering light shines, the more the led fades. If the bend lighting is 100% illuminated, the LED goes out completely.
    The second problem is that if there is an LED, the turn signals on the left are slightly glowing - they do not want to go out and the interrupter goes crazy and flashes quickly.
    The third problem is that after two or three minutes of driving the LED has been damaged (i.e. lights up, but as if only at 10% of its power and does not want to shine more). The first time I sent back for warranty, because I thought the LED was whacked factory, but they sent me a new one and it turns out that the history repeated itself - 2 minutes of driving and the LED dims and shines for about 10% of what it should.
    The LED on the right shines nicely, strongly and there are no problems with it

    Anyone can do something?
    Where to find the reason
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  • #2 16939375
    piotrekwoj1
    Level 43  
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    In this trash what you bought. Your CANBUS is a great g..no because there is no such thing is just an advertising gimmick. Is everything ok?
  • #3 16939434
    iDest
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    On normal bulbs, everything is OK.
    So what? I have shit LEDs?

    I was already looking for other LEDs. I found it cool and very bright. The cost is PLN 200. And the problem is not the cost, but how can I be sure that the car will not damage me such an expensive LED?
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  • #4 16939476
    Strumien swiadomosci swia
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    iDest wrote:
    I found it cool and very bright. The cost is PLN 200. And the problem is not the cost, but how can I be sure that the car will not damage me such an expensive LED?

    In the case of PWM control with drivers, LEDs should not be used.
    If you already have to buy Osram or Philips bulbs.
  • #5 16939616
    Gerri
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    Put this good LED on the other side and after two minutes you will know everything.
  • #6 16940110
    iDest
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    Gerri wrote:
    Put this good LED on the other side and after two minutes you will know everything.


    On the right side is also cornering light (controlled by PWM) and everything works

    Why is the LED on the left damaged?
    What is the reason for this? What phenomenon
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  • #7 16940310
    Strumien swiadomosci swia
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    iDest wrote:
    What phenomenon

    This phenomenon is poor product quality.
  • #8 16940549
    pp_pablo
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    So out of curiosity I ask why you replace bulbs for leds?
  • #9 16940661
    iDest
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    Because the usual H7 has 1500 lumens, and one LED has 3600 lumens (although there are also 8000lm per bulb).

    At the moment I drive on one led (because I do not have H7 to replace) and I will say that one LED shines better than two ordinary H7 (I have lens headlights)

    That's why I insist on LEDs, because they shine much better than regular H7
  • #10 16940674
    Strumien swiadomosci swia
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    Then install a 4700 micro 35V capacitor in parallel with the bulb's power supply to calm down the power supply.
  • #11 16940684
    iDest
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    Strumien swiadomosci swia wrote:
    Then install a 4700 micro 35V capacitor in parallel with the bulb's power supply to calm down the power supply.


    Couldn't be smaller? (e.g. on 16-18V)?
  • #12 16940696
    Strumien swiadomosci swia
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    iDest wrote:
    Couldn't be smaller? (e.g. on 16-18V)?


    If you don't want it fried, put it on 35V.
  • #13 16940703
    iDest
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    So I will.
    Will this protect the LED against damage in some way?

    Because the one that came back from the warranty, before I put it in the car, walked for several hours connected to a 12V battery and shone beautifully.
    And in the car 2 minutes and fell (shines as if at 10% power).
    Someone will explain to me why this happened and how to protect yourself from it?
  • #14 16940708
    Strumien swiadomosci swia
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    iDest wrote:
    Someone will explain to me why this happened and how to protect yourself from it?


    I wrote you that you don't have constant voltage in the car, only PWM. What else.
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  • #15 16940780
    Gerri
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    iDest wrote:
    Gerri wrote:
    Put this good LED on the other side and after two minutes you will know everything.

    Why is the LED on the left damaged?

    You didn't get it. If this good LED goes down two or three minutes after putting it to the left side, the car is to blame. If it shines - the poor quality of these LEDs is to blame.
    iDest wrote:
    Because the one that came back from the warranty, before I put it in the car, walked for several hours connected to a 12V battery and shone beautifully.
    And in the car 2 minutes and fell (shines as if at 10% power).

    The battery gives 12V, the car has 14.4. In the case of semiconductors (in this case LED) an increase in voltage by tenths of a volt can generate avalanche increases in current consumption. We know how Chinese inventions work - on the verge of safe use. In the specification they write that "at 12V they take some mA ...
    In the case of complaints they will answer that "it's written 12V" and not 14.
    iDest wrote:
    At the moment I drive on one led (because I do not have H7 to replace) and I will say that one LED shines better than two ordinary H7 (I have lens headlights)

    That's why I insist on LEDs, because they shine much better than regular H7

    A few days ago I put H1 LED headlights. So more on trial and not so low-end SMD. They went into the traffic lights so as not to dazzle. The impressions are that glowing diodes cannot be considered as a point source of light which is the filament of a halogen bulb. Three diodes in a row are about 3mm. The diodes on both sides of the heat sink are separated by a distance of approx. 2-3 mm. Yes, light is much more intense than with halogen. But only near the headlight. Because the beam is not focused like a light bulb and as the distance increases, the light intensity catastrophically decreases. Spotlights give up trees, left and right fields - what should be a focused beam scatters to the left, right, up and down. Color also does the job, because LEDs with a lower light temperature guarantee much better visibility. It's cool to blink someone blue, but visibility (especially in the case of "wet" weather) is definitely better in lights more similar to white / yellow.
  • #16 16940976
    iDest
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    Quote:
    The battery gives 12V, the car has 14.4. In the case of semiconductors (in this case LED) an increase in voltage by tenths of a volt can generate avalanche increases in current consumption. We know how Chinese inventions work - on the verge of safe use. In the specification they write that "at 12V they take some mA ...
    In the case of complaints they will answer that "it is written 12V" and not 14


    The LEDs that I bought in the specification have a supply voltage of 9-32V.

    Will be buying some better and more expensive soon. I'll put the capacitors and see how it goes

    Quote:
    How many days ago I put the H1 LED headlights. So more on trial and not so low-end SMD. They went into the traffic lights so as not to dazzle. The impressions are that glowing diodes cannot be considered as a point source of light which is the filament of a halogen bulb. Three diodes in a row are about 3mm. The diodes on both sides of the heat sink are separated by a distance of approx. 2-3 mm. Yes, light is much more intense than with halogen. But only near the headlight. Because the beam is not focused like a light bulb and as the distance increases, the light intensity catastrophically decreases. Spotlights give up trees, left and right fields - what should be a focused beam scatters to the left, right, up and down. Color also does the job, because LEDs with a lower light temperature guarantee much better visibility. It's cool to blink someone blue, but visibility (especially in the case of "wet" weather) is definitely better in lights more similar to white / yellow.


    I want to insert H7 into the lens, and it's quite different from a classic reflector without a lens
  • #17 16941207
    tzok
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    iDest wrote:
    I want to insert H7 into the lens, and it's quite different from a classic reflector without a lens
    Which does not change the fact that these LED "bulbs" are not approved and must not be used. If you participate in a traffic incident, you run the risk of getting compensation.

    Your description indicates a corroded ground connection in the left lamp.
  • #18 17269344
    Ufokkk
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    iDest have you covered the topic of these LEDs?

    I still have a question - you could easily fit LEDs with fans in Mondeo MK4? - I mean, if caps can be easily put on, even though the LEDs have a larger "ass" than standard bulbs.
  • #19 17278545
    iDest
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    Fit fit.
    I haven't solved the problem yet. I am looking to buy much better and more expensive LEDs. Maybe they can do it
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Topic summary

✨ The discussion revolves around issues faced by a Ford Mondeo MK4 (2008) owner after replacing standard H7 bulbs with LED H7 Canbus bulbs. The left LED experiences fading and complete failure when the cornering light is activated, while the right LED functions correctly. Users suggest that the problems may stem from poor product quality, PWM control issues, or a corroded ground connection. Recommendations include using reputable brands like Osram or Philips, installing capacitors to stabilize voltage, and considering the specifications of the LEDs, which should support a voltage range of 9-32V. The owner is contemplating purchasing higher-quality LEDs to resolve the issues.
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FAQ

TL;DR: Mondeo MK4 LED H7 issues often come from PWM control and 14.4 V system voltage—"The battery gives 12V, the car has 14.4." [Elektroda, Gerri, post #16940780]

Why it matters:** This FAQ helps Ford Mondeo MK4 owners fix fading, hyperflash, and premature LED failure in projector/cornering light setups.

Quick Facts

Why does my left H7 LED fade when the cornering light turns on?

Your left lamp likely gets PWM-modulated power when the cornering function activates, starving the LED driver. LEDs expect stable DC; PWM without proper buffering makes them dim or shut off. As one expert put it: “you don’t have constant voltage in the car, only PWM.” Adding input smoothing can help. [Elektroda, Strumien swiadomosci swia, post #16940708]

Can PWM actually damage cheap LED H7 bulbs?

Yes. Many low-cost LED H7 kits have weak drivers. Rapid PWM pulses and higher system voltage heat the driver and chips. That can degrade output within minutes, as reported. An experienced member advised not to use such LEDs “in the case of PWM control with drivers.” [Elektroda, Strumien swiadomosci swia, post #16939476]

How do I test whether the car or the bulb is at fault?

Swap the known-good LED to the problematic side and drive for two minutes. If it fades or fails, the vehicle side or wiring is implicated. If it stays bright, the original LED was poor quality. This quick A/B test isolates the fault without new parts. [Elektroda, Gerri, post #16939616]

Could a bad ground in the headlamp cause these symptoms?

Yes. A corroded or high‑resistance ground on the left lamp can cause cross‑feed, dimming, ghost glowing of turn signals, and erratic flashing. Clean and retorque the ground points and connectors before replacing electronics. Poor grounds often mimic CAN or PWM faults. [Elektroda, tzok, post #16941207]

What simple fix can stabilize power to my LED H7 on a PWM circuit?

Add a smoothing capacitor across the bulb’s supply. A 4,700 µF electrolytic wired in parallel helps convert PWM to steadier DC for the LED driver. Install close to the lamp for best effect. This reduces flicker and fading during cornering light activation. [Elektroda, Strumien swiadomosci swia, post #16940674]

What voltage rating should that capacitor have?

Use 35 V. Automotive transients exceed 16–18 V, and a 35 V capacitor provides needed headroom against spikes. As one expert warned, “If you don’t want it fried, put it on 35V.” Choose quality, low‑ESR parts rated for heat. [Elektroda, Strumien swiadomosci swia, post #16940696]

Why did my LED work on a 12 V battery but fail in the car?

Bench tests at 12 V miss in‑car stress. The alternator outputs about 14.4 V and the body module may apply PWM. That extra voltage and pulsing can push marginal drivers into thermal or current overload. “The battery gives 12V, the car has 14.4.” [Elektroda, Gerri, post #16940780]

Are LED H7 retrofits brighter than halogen in the Mondeo MK4 projector?

One user reported halogen H7 at about 1,500 lm versus claimed 3,600 lm for a single LED. However, beam quality matters more than raw lumens. Poor emitter geometry can scatter light and reduce down‑road visibility, especially in wet conditions. [Elektroda, iDest, post #16940661]

Why are my left turn signals glowing slightly and hyperflashing with LEDs installed?

Ghost glow and fast flash point to wiring or grounding issues on that side. Current can backfeed through shared grounds or modules when LED loads change circuit behavior. Inspect, clean, and repair the left lamp ground and connectors first. [Elektroda, tzok, post #16941207]

Is “CANBUS” printed on LED bulbs a real fix for errors?

Not necessarily. Many kits labeled “CANBUS” only add resistors and do not communicate on the car’s CAN network. They often fail to stop warnings or hyperflash. A seasoned member called it an “advertising gimmick.” [Elektroda, piotrekwoj1, post #16939375]

Are LED H7 retrofits legal in halogen housings on this car?

No, not when the lamp lacks approval for LED sources. Using non‑approved LED “bulbs” in halogen projectors can fail inspection and risk liability after a crash. Revert to approved halogen or use certified LED systems. [Elektroda, tzok, post #16941207]

Will fan‑cooled LED H7 bulbs fit under the Mondeo MK4 headlamp caps?

Yes. Owners reported that fan‑based H7 LED retrofits do fit and the rear caps can still be installed. Always check depth and cable routing before final assembly to avoid strain on connectors. [Elektroda, iDest, post #17278545]

What does PWM mean here, and why does it matter?

PWM (pulse‑width modulation) rapidly switches power on and off to control lamp brightness, such as cornering lights. Some LED drivers misbehave on PWM feeds, causing visible fading or damage unless buffered. Avoid LED retrofits on PWM, or add smoothing. [Elektroda, Strumien swiadomosci swia, post #16939476]

How can I install the smoothing capacitor safely (3 steps)?

  1. Disconnect battery negative and remove the headlamp cap.
  2. Solder a 4,700 µF 35 V electrolytic across the lamp’s + and − leads, observing polarity.
  3. Insulate, secure the capacitor near the connector, reassemble, and test. [Elektroda, Strumien swiadomosci swia, post #16940674]

What’s the edge case I should watch for after the fix?

If the LED still dims or the indicator glows after smoothing, suspect a degraded ground on that side. Clean the ground lug and inspect for corrosion or damaged wiring to prevent recurring faults. [Elektroda, tzok, post #16941207]

Will paying more for "9–32 V" LEDs guarantee reliability here?

Not guaranteed. Even wide‑input drivers can fail under 14.4 V plus PWM ripple and heat. Verify performance in‑car after installation, and keep receipts. High claims without approval or testing often disappoint. [Elektroda, iDest, post #16940976]
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