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Porsche 911 SC, SAAB SPG
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 308
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Melted a ground wire going to fuel level gauge
Well, I was testing out all of the lights on the car when suddenly I got a whiff of that tell-tale smell and then the smoke started pouring out of the dash.
I quickly disconnected the battery and felt around for the hot wires in the dash. I can only find the one melted wire and I don't really understand how the short occured. The wire is a ground wire that goes from the fuel gauge to the oil pressure gauge. It is connected in series with the ground to the fuel level sender and then moves on to the tach. None of these other ground wires seem to be burned. My only guess is that there was some shielding problems with this one wire and it shorted itself somehow. I have done a thorough inspection of the headlight switch and I cannot find any other burned wires. I can't figure out where the battery power came from to cause the short. I also have already installed the 3amp fuse on the dash lights so that wasn't the problem. I would like other opinions on this as I don't want to burn the car down just replacing the wire and hope the problem was just an insulation issue.    Thanks for any input!
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Jeff C |
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05-29-2008, 07:31 AM
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Join Date: Apr 2005
Location: outta here
Posts: 53,250
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Probably wasn't a ground wire.....grounds shouldn't short out against the chassis.
I'd start with a wiring diagram to see what the wire really was. JR |
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05-29-2008, 08:01 AM
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Porsche 911 SC, SAAB SPG
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 308
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I agree that grounds don't short against the chassis. My guess is that either the gauge itself or the ground wire touched a power wire. I just can't figure out which power wire...
The melted wire is/was brown and is connected with many other brown wires in series, so it is definitely a ground wire.
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Jeff C |
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05-29-2008, 09:48 AM
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Join Date: Apr 2005
Location: outta here
Posts: 53,250
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What car are we talking about?
JR |
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05-29-2008, 10:37 AM
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Join Date: Jan 2002
Location: Long Beach CA, the sewer by the sea.
Posts: 37,740
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Pics w/o labels are difficult. All I see is a toasted red wire. That ain't no ground.
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05-29-2008, 11:12 AM
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Porsche 911 SC, SAAB SPG
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 308
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Okay, I have an update on the hunt.
I have found the ground wire that is supposed to be ground, but is really 12 volts. Based off of the wiring diagram, it seems to be coming from the rear defroster switch. Interesting is that it seems as if the ground wire for this switch connects into the oil level gauge... I have no idea how this switch works however. If I have the switch pushed in and turned left, the ground wire is fine and does not short. If I have the switch pushed in and turned right, then the ground wire becomes 12 volts. If I pull the switch out, then the ground wire becomes 12 volts. I'm also attaching a better pic with some labels. However at this point I just need to know what the switch is supposed to do in the different selections. 
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Jeff C |
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05-29-2008, 11:44 AM
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Porsche 911 SC, SAAB SPG
Join Date: Sep 2007
Location: Charlotte, NC
Posts: 308
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Ok. Short has been located and eliminated.
I can't even blame this one on bad factory wiring! So, when I got the car it had just been painted and the door mirrors were off of it. I guess when you take off the mirrors, you need to pull the wires out of the plug so you can push the wires back into the doors. The painter just wrapped all of the door wires up together with tape. Hence, when the defroster switch was turned on, the 12 volts for the heated mirrors went down all of the wires, one of which is the ground wire... At least now I know where the heated mirror switch is located!  Now to go fix the damage.
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Jeff C |
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05-29-2008, 12:24 PM
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Whew! You had us going there for a minute..........
All I could think of was what Milte said.......... Was looking forward to a ground scheme/distribution review (Bentley nearby) ...... good to do over a very fine French wine while blasting some RUSH..... That part about the car being VERY recently painted (and APART) would have been good data for post #1... Glad you found it!!! Best,
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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05-29-2008, 12:56 PM
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AutoBahned
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painters are artists
that has good and BAD aspects. IMHO, letting a painter near electrical wires is asking for trouble -- just like letting a wood carver run rampant in a machine shop... |
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05-29-2008, 01:22 PM
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Quote:
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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05-29-2008, 02:33 PM
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...wait,..maybe that's a good thing.
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Recording Engineer, Administrator and Entrepeneur Designer of Fine Studios, Tube Amplifier Guru 1989 Porsche 911 Carrera Coupe 25th Anniversary Special Edition Middle Georgia |
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05-29-2008, 02:33 PM
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AutoBahned
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"letting a machinist run rampant in a wood shop..."
AH! But who sets up the machines every season? A type of machinist, called a "mill wright." |
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05-29-2008, 03:12 PM
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