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2002 GMC SIERRA 2500HD LB7
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Discussion Starter · #1 ·
i traded the truck for my 03 6.0 its a 2002 GMC SIERRA 2500 crew cab short bed. the radio didn't work so i pulled it out and took a look at the wiring only to find half the wires weren't even hooked up. after rewiring the radio it worked fine for a day ish. i went to my local reservoir for some pictures and my entire dash started smoking i quickly jumped out of the truck and disconnected the battery, then i started looking where it started from i found it completely melted the ground wire coming into my firewall from the engine bay, since then my truck has been stuck in 2/3 wont shift no radio no cluster and some other small issues? what would of caused this to melt? and any ideas on how much to replace the harness/labor any help would be greatly appreciated!
 

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Looks like some part was on top of the wiring, rubbed/crushed it, broke the insulation and you had a short. That's what it looks like to me.
 

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Discussion Starter · #4 ·
Looks like some part was on top of the wiring, rubbed/crushed it, broke the insulation and you had a short. That's what it looks like to me.
Thanks for the information i'll take a look into it deeper tomorrow
 

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Discussion Starter · #5 ·
so a quick update it's not the ground wire it's a constant 12v pink wire that burnt? any ideas on why that would of happen ?
 

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Like Ron said, one wires probably has a crack or break in the insulation. Even a pin hole in a power wire could cause an arc to another wire that had a crack. Electricity always looks for the simplest path to travel, and if that means jumping through a small hole to another exposed wire, it will. It older wire, and unfortuantely happens. Repair them all correctly and protect them best you can from water and each other.
 

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Discussion Starter · #7 ·
Like Ron said, one wires probably has a crack or break in the insulation. Even a pin hole in a power wire could cause an arc to another wire that had a crack. Electricity always looks for the simplest path to travel, and if that means jumping through a small hole to another exposed wire, it will. It older wire, and unfortuantely happens. Repair them all correctly and protect them best you can from water and each other.
Thanks you! would you happen to have a diagram of the harness?
 

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Unfortunately, ull probably need to cut out the burnt portion, looks like several wires, and just got soldering. Just do one at a time, color to color, don't skimp, solder, heat shrink, repeat, u don't need to get factory wire, just a few feet of proper guage, maybe one guage thicker. If u don't solder, its a quick learn. Take ur time, do it once. And everything that stopped working will be right as rain, unless u popped a fuse. Sorry that's my only advice.
 

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My other advice, unhook anything u did before this happened. It sounds like u connected something with power to another power source creating too much current, which that small wire couldn't handle. That wire is only good for 10-15 amps, so u may have inadvertently hooked 2 things together incorrectly. So be sure to undo everything u did, wire up ur burnt wires, then start over with the radio.
 

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Thanks you! would you happen to have a diagram of the harness?
I don't think I have ever seen a diagram of the harness per se. But wiring diagrams, which are logical, not physical, are available here: GM UPFITTER - Body Builder Manuals Look for the ELECTRICAL MANUAL for your year and model of truck.
 

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Discussion Starter · #11 ·
thank you guys for all the help it’s much appreciated what’s the easiest way to pull the harness out of the firewall?
 

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You don't want to pull the harness out of the firewall.
First step is to isolate the broken/burnt wire(s) and open up the harness by cutting the wrapping. Then attach a new piece of wire, same size, where the problem area is, removing the actual burnt or arcing part of the wire. You can do that with WAGO lever nuts on each end BUT this is just a test to make sure the fix is actually a fix to the problem, not just one of many. . Run the truck for a while (week or two or longer but not forever) with the WAGO's to make sure all is OK. If this new wire actually fixes all of the problems, then you need to either solder the connection (best choice) or use crimp connectors (2nd choice), and retape the harness.
 
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I don't think anything is arc'ing out at 12 V to ground. It's probably just worn insulation between two adjacent wires or between the hot wire and a piece of metal. A small enough contact patch will have high enough resistance that instead of blowing the fuse it'll just get insanely hot.

Like @Ron Nielson said, just fined the damaged wires and splice in some good wire. Once you're confident that things are working properly tape it back up and you're all set. Personally I prefer heat-shrink butt connectors for this sort of thing; they're easy to install and provide good protection against oxidation and the elements.
 

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Discussion Starter · #14 ·
so the issue i'm running into is, the burnt wire runs from my main fuse box under the hood then runs thru the firewall then goes into the fuse box on side of the dash? how would i replace that entire wire thru the firewall without removing it? i'm sorry if this doesn't make sense i'm new to forums
 

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so the issue i'm running into is, the burnt wire runs from my main fuse box under the hood then runs thru the firewall then goes into the fuse box on side of the dash? how would i replace that entire wire thru the firewall without removing it? i'm sorry if this doesn't make sense i'm new to forums
The only part you need to replace is the part that has insulation worn off it. If it's too close to the firewall you may have to run new wire, but I wouldn't try to remove the entire wiring harness. I would just cut the wire on one side of the firewall with enough length left that you can connect a new piece of wire with a square knot and electrical tape, then yank it through to the other side so that your new wire is through the firewall. Then use heat-shrink butt connectors to splice it all together. Obviously you'll need one on each side of the firewall if you do it this way.
 

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Discussion Starter · #16 ·
The only part you need to replace is the part that has insulation worn off it. If it's too close to the firewall you may have to run new wire, but I wouldn't try to remove the entire wiring harness. I would just cut the wire on one side of the firewall with enough length left that you can connect a new piece of wire with a square knot and electrical tape, then yank it through to the other side so that your new wire is through the firewall. Then use heat-shrink butt connectors to splice it all together. Obviously you'll need one on each side of the firewall if you do it this way.
Alright i'll get on it this weekend and will keep everyone updated! i went out to move my truck to the sun and i have no throttle and no cluster now and a P1639 Code. 5 Volt Reference 2 circuit and U2106.
 

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BINGO!! You've found the mother lode. Buy a lottery ticket, quick.

And congratulations on finding your problem and posting it.
 
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