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> Fog lights not working, calling all electricians
malcolm2
post Sep 28 2014, 02:26 PM
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OK, I know enough about elec. to test a few things so here is what I found once home from Okteenerfest.

Fog lights, driving lights, whatever you want to call them just quit working.

The pull knob lights up
I get 12v in the front trunk at the connection from the main harness. (that is with the connection separated) {with all wire connected, I get no reading}
Grounds have continuity there too.

I did not get 12 volts once I took the light apart, not the bulb holder, just the light was apart and I used an alligator clip to ground it. No volts.

If I remove the alligator clip from the hanging light in the picture below and put the red lead of the VM on the white/ylw wire at the bulb holder THEN the black lead of the VM to a bolt on the car..... I get 12 volts.

So with the bulb holder or the complete fixture assembled and grounded I get nothing.

What is going wrong here?

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Tom
post Sep 30 2014, 06:51 AM
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So it was a bad/dirty connection? Seem to remember saying check those in post #4.
Glad you finally found it.
As to exactly why you were reading voltage in post #1, but getting no fog light when you connected them: with no ground hooked to the end of the fog light circuit ( the bulb was not in the circuit and the normal path to ground is thru the bulb to ground) this is an open circuit and all points of the + circuit will read battery voltage. When you hooked the bulb into the circuit, that did make a complete circuit to ground, however, the bad connection at the relay was dropping all or most of the voltage across it instead of across the bulb.
Now, why did the relay socket melt. Power dissipation in a very small area that had no way to deal with the heat. It should have been 0 ohms and then there would be no power dissipation across that connection and no heat build up. Why power dissipation? Because the bad connection was not always so bad (high ohms across the connection). When it was a lower ohms connection, say 1 or 2 ohms, it was causing 36 watts at 1 ohm and 18 watts at 2 ohms to dissipate in that small area. As the heat built up, the connection rapidly failed to a much higher resistance due to the heat causing oxidation and plastic/rubber contamination and possible arcing resulting in even more heat.
That's why I said in post #4 Check up stream for all connections, ensure they are clean and tight.
Well, that's my story anyway,
Tom
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Posts in this topic
malcolm2   Fog lights not working   Sep 28 2014, 02:26 PM
messix   is there continuity on the ground of the socket [o...   Sep 28 2014, 02:39 PM
malcolm2   is there continuity on the ground of the socket [...   Sep 28 2014, 03:13 PM
messix   is this a sealed beam light?   Sep 28 2014, 02:45 PM
Tom   Sounds like you have a bad/dirty connection that ...   Sep 28 2014, 03:06 PM
Mike Bellis   If you read 12V on the ground lead, through the la...   Sep 28 2014, 03:07 PM
malcolm2   If you read 12V on the ground lead, through the l...   Sep 28 2014, 03:33 PM
malcolm2   If you read 12V on the ground lead, through the l...   Sep 28 2014, 03:42 PM
Dave_Darling   Strangely enough, I do NOT get continuity between...   Sep 28 2014, 03:47 PM
malcolm2   OK, must have been something in my rig from the ba...   Sep 28 2014, 04:51 PM
Mike Bellis   If you have 12V to the light, the problem is with ...   Sep 28 2014, 04:53 PM
malcolm2   If you have 12V to the light, the problem is with...   Sep 28 2014, 05:00 PM
76-914   Look at the bulb carefully to see if the tungsten ...   Sep 28 2014, 05:03 PM
malcolm2   Look at the bulb carefully to see if the tungsten...   Sep 28 2014, 05:13 PM
76-914   Look at the bulb carefully to see if the tungsten ...   Sep 28 2014, 05:07 PM
messix   check and clean contacts on fuse 10   Sep 28 2014, 05:09 PM
messix   do you have amp draw feature on you vom? if you d...   Sep 28 2014, 05:24 PM
malcolm2   do you have amp draw feature on you vom? if you ...   Sep 28 2014, 05:47 PM
malcolm2   J5 Is the one. Bowlsby had it.   Sep 28 2014, 05:53 PM
malcolm2   :bump: for more conversation and some results. I...   Sep 29 2014, 06:13 PM
malcolm2   My guess on operation: When turned on and on low b...   Sep 29 2014, 06:16 PM
malcolm2   One more bump... No action on electrical issues t...   Sep 29 2014, 08:40 PM
messix   corrosion on contacts make a high resistance and c...   Sep 29 2014, 09:11 PM
malcolm2   corrosion on contacts make a high resistance and ...   Sep 29 2014, 09:22 PM
messix   corrosion on contacts make a high resistance and...   Sep 29 2014, 10:22 PM
Mike Bellis   Most likely cause of the melting was a loose conne...   Sep 29 2014, 10:18 PM
914Mike   Check the pins on your relays. If you look closely...   Sep 29 2014, 10:48 PM
malcolm2   Check the pins on your relays. If you look closel...   Sep 30 2014, 05:49 AM
Tom   So it was a bad/dirty connection? Seem to remember...   Sep 30 2014, 06:51 AM
malcolm2   So it was a bad/dirty connection? Seem to remembe...   Sep 30 2014, 02:10 PM


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