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We've had intermittent reports that a headlight was out on one of our Jettas. Both have aftermarket "eurospec" headlamps with fog lights from ECS Tuning. They claim to be Hella lights, but could well be forgeries.

Today, I finally caught the light being out and decided to replace the bulb. When I pulled the bulb I noticed that the connector was slightly melted at the low beam ground terminal (the one between the two parallel side terminals) and that both filaments seemed to be intact. I confirmed that the bulb as good and tightened up the flag connector on the melted terminal.

The lights are working again, but I'm wondering. Are there other possible explanations of the heating / melting besides a loose connector?

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  • Are you sure the melting is new? Could possibly caused by an old bulb?
    – Iman Nia
    Dec 4, 2016 at 23:59
  • Pretty sure. I don't recall noticing it when I put in the current bulb and it is only the second bulb since I installed the aftermarket lights.
    – dlu
    Dec 5, 2016 at 0:03
  • One way I know the melting is associated with the current bulb is that there are drips of plastic on the bulb terminals. Just remembered that.
    – dlu
    Dec 5, 2016 at 7:02

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Following reasons could melt your connector :

  1. Loose connection, this will increase resistance producing much more heat. Most of the time a loose connector could be the problem but a loose connector itself is produced by an overheated bulb. So if you think all of the cars that complaining do have a loose connector that would be the case but I do not think this the main reason.

  2. Using a bulb with much higher nominal power, people do this most of the time however using a 55watt headlight instead of a 35watt standard usually get tolerated by wiring system but it depends on other parameters.

  3. Cheap bulbs with higher resistance than expected, cheap bulbs create more heat, you may measure the bulbs resistance using an ohm meter. Sometimes you may be surprised! Bulbs must have 2 ohm resistance, if they are 2 ohm with a bit higher or less then there is nothing wrong with your bulb go find the main culprit. But if they are higher than 3 ohm, this is it! However if your bulb resistance is about 2.7 then it may help connector to loose and they together could melt the connector.

  4. No air ventilation, bulbs produce heat and they should be cooled down somehow, some have heat sink, some dont! There is some model of h4 bulb that came with a heat sink and a wire connecting it to the connector, I recommend to use these kind of bulbs instead of traditional models, however the old fashioned bulbs also have a metal neck which plays a heat sink role. In all cars there is a little hole on light box which is there to circulate the heated air inside the light, check if they are blocked.

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  • can you post a photo or link to what that hole on the light box looks like? I'd like to go identify one on mine if possible.
    – jxramos
    Jan 11, 2021 at 6:48
  • @jxramos Sorry, I can’t. I sold that car 😊
    – Iman Nia
    Jan 11, 2021 at 9:17
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the melting is caused by excessive heat - usually by a loose connection. Check that the terminals grip tightly.

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  • There may also be a corrosion film that adds resistance; it is very easy to wipe the terminals with sandpaper, or similar.
    – blacksmith37
    Jun 12, 2020 at 15:20

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