Fog lights not working, calling all electricians |
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Fog lights not working, calling all electricians |
malcolm2 |
Sep 28 2014, 02:26 PM
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#1
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Advanced Member Group: Members Posts: 2,745 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
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? |
Tom |
Sep 30 2014, 06:51 AM
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#2
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Advanced Member Group: Members Posts: 2,139 Joined: 21-August 05 From: Port Orchard, WA 98367 Member No.: 4,626 Region Association: None |
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 |
malcolm2 |
Sep 30 2014, 02:10 PM
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#3
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Advanced Member Group: Members Posts: 2,745 Joined: 31-May 11 From: Nashville Member No.: 13,139 Region Association: South East States |
So it was a bad/dirty connection? Seem to remember saying check those in post #4. Glad you finally found it. 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 My limited experience with voltage left me not thinking of the relay as a connection. So in my mind, there were no more connections from the harness in the front trunk to the relay. All of those had been checked. So I planned to eventually drop the fuse panel and check the connections on the switch, still not thinking of the relay as a connection. But I did know the relay was a possible failure point. Well it obviously is a connection, something that I will look at sooner next time for sure. (IMG:style_emoticons/default/shades.gif) I'll put my hands on this in an hour or so and see if I can make good tight connections at that lightly melted plug. Fingers are crossed! UPDATE: cleaned the brittle rubber or plastic from the melt, pinched the "rings" on the socket that connect to the relay and I spread the pins in the relay. Also used some emory cloth and cleaned the pins and the inside of the relay socket rings. Put my light back together and turned it all on. Hit the high beams 10 or 12 times and everything is working fine. Thanks again. |
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