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Volkswagen Jetta, Golf, GTI: 1999-2005, R32: 2004 (A4) headlight switch melting wire


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Last Post: Nov 8, 2013 1:30 PM Last Post By: bobbassplayer
LexDube

Posts: 2
Registered: 08/14/12
headlight switch melting wire
Posted: Aug 31, 2012 10:36 PM
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I have a problem, I can't turn on my headlights. If I do so, the lights turn on but the wires start overheating and smoking inside... how can I fix that?

I am on the stock bulbs

Edited by: LexDube on Aug 31, 2012 10:36 PM
tcovenant2000

Posts: 1,750
Registered: 12/09/03
Re: headlight switch melting wire
Posted: Sep 6, 2012 5:42 PM   in response to: LexDube in response to: LexDube
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Likely you have a short somewhere at the bulb end. Probably a wire has rubbed and is shorting to a dirty ground, so it's not a clean short. Still, if the wires are melting, one must first ask what fuses are in your fusebox. Can you verify what amp fuses are in the spots where the headlight fuses go?
The proper way to troubleshoot this is with a 100A ammeter. Remove the headlight fuses. Put the ammeter across the fuse terminals for each headlight, one at a time, turn on the headlights and note the amperage reading. I'm not sure what the correct current is, but you could ohm the bulbs (without the wires connected) and do the math. If you're seeing much higher current on one bulb than on the other then you've found where to start looking. If both are high, possibly you have a short somewhere in the switch area.
What about the high beams? Do those also smoke wires?

Thomas
bobbassplayer

Posts: 22
Registered: 01/13/08
Re: headlight switch melting wire
Posted: Nov 8, 2013 1:30 PM   in response to: LexDube in response to: LexDube
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If the lights come on, you don't have a short circuit. Instead, you probably have a poor electrical connection (corrosion, dirt, etc.) or someone installed undersized wire (especially if the car was previously owned by someone who liked to tinker but didn't know what they were doing).

Either situation will result in excessive resistance for the amount of current that has to pass through it. This will reduce the voltage and current delivered to the lights and also cause a large amount of power to be dissipated as heat in that resistance. Wherever the heating (smoke) is occurring, that's where your problem is.

For example, your alternator might be putting out 14.0 volts DC but because of a bad connection at some point in the headlight wiring, the headlights themselves are only getting 11.0 volts. Let's say the headlights are drawing 12 amps of current. Then 3 volts 12 amps = 36 watts of power being turned into heat at that point where the bad connection is. It's not a huge amount of power but it's concentrated into a small point, so it heats up like a small soldering iron at that location. And that's what causes the smoking and overheating you experience.

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