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Ok, so this was my daily driver and here what happened and how i probably ruined the vehicle.

A week ago i was driving to work and the battery light came on and a bunch of red sensors *oil temp and others*

I get to work, open the hood and notice the fuse box is melted and the alternator wiring harness wire has melted so bad that it severed the connection!

Okay so i have AAA tow it home....here we go..

I order a fuse box (the proper one, i believe, got it off ebay (this one For 1999 2004 VW Jetta Golf MK4 Beetle Fuse Box Battery Terminal 1J0937550A B | eBay)

and i read online that the alternator wiring harness can degrade to the point of getting hot enough to melt the fuse box so i order some 4 guage wire to (maybe) replace the alternator wire with ...

the fuse box came in today, i figured i'd connect everything with the original wire to see if that "fixed" the problem and would take the alternator wiring harness off if it started to get hot again.

So i connect the fuse box and screw everything down really tight, all connections in their original places and then try to turn on the car but the dash acts like it has like barely enough power to even display the mileage..

HERE IS WHERE I MESSED UP AND THINK I SHOULD SELL IT FOR SCRAP

I tried to jump the car to see if the battery just happened to be dead and the alternator started SMOKING and smelling horrible. so i disconnect the jumper cables and now, no lights no nothing...car is deader than it was before.

Am i screwed here? did i just fry the alternator on top of the other issues?
 

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Well, you definitely have a electrical issue; the question is, what was causing it? My first thought; is that your alternator or the charge wire is grounding out or the regulator is stuck on all the time. If you have wiring; that is melted; you had a SERIOUS draw; that cause it to get so hot, everything melted. Don't freak out and scrap the car; just like any repair: there is a problem and you just need to fix the source of the problem, replace any damaged parts. Done.

I would remove all of the melted wiring and related components; replace all the wiring and have each component (e.g. battery, alternator, etc.), checked/tested to see if they are bad. Then, put everything back together with good wiring and parts; test the charging system and confirm it is charging correctly, see if any of the wires get hot and hopefully, you have fixed the issue. Other components; such as cooling fans, are known to go bad and cause the fuse box to melt as well. So, you need to confirm; that all these things are ok and not causing the large amperage draw.

Check out these replacement fuse boxes; by Tech Smart and watch the video as well:

https://www.youtube.com/watch?v=sQA4JKp8DVQ&list=PLr6bMjaylF1SOEbX1Jj-sC7mYI3jd6Jai
 

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I'm having the same problem and have been reading post for about 6 hours now. It seems to be a common problem with different causes. In my case it is only the alternator wire that is heating up. I have checked the alternator with a multimeter that has a memory. The largest voltage I get is 13.4 and also took it to the autoparts store and had it bench tested. tested good. The battery has also tested good by me and the parts store. I have since checked the ground underneath the battery box and it seemed clean but I cleaned it anyway. I'm at a real lose here. Ive melted my third fuse box in 3 days. My next step would be to replace the harness, but is it necessary? Can I just replace the one wire or do the connectors that attach to it feed from that wire? I'm also going to order an upgraded fuse box by Tech smart but I don't want to melt it too if the source hasn't been resolved.

BTW a quick solution to get home if your desperate is to hook the alt wire straight to the battery. Its only a temp fix, but it has gotten me home 3 time now!
 

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At this point; you are trying to find the SOURCE of the draw and the charge wire from the alternator is one of the biggies, too much internal corrosion and resistance (causing increased amperage/heat). Check out this company; for their harness replacements and you could buy it from them or use their kits as a guide to make your own. As noted before; failing cooling fans, are the other classic issue to cause problems.

Voltage drop testing; seems, to be the best way to test resistance in the related wiring harnesses.

Lots of good info and videos:

https://www.youtube.com/results?search_query=automotive+voltage+drop+test

https://www.google.com/search?q=aut...ome.0.69i59.1781j0j4&sourceid=chrome&ie=UTF-8

Because, of the amount of problems you have had; replacing all the charging and ground harnesses, might be a good idea. You are spending allot of money on new fuse boxes; so the cost of the innovative wiring kit, would actually be saving you money. I had my fuse box, melt once and I have been tempted to replace all the harnesses and make my own, for awhile now. It all comes down to time and money; pay him for his kit or take the time, to make them yourself. Let us know; what you end up doing. Thanks! :)

Volkswagen | Innovative Wiring LLC

If you look; at the stock wiring harnesses compared to the innovative wiring kits, you can definitely see the difference in the wire gauge! While, he is in the business; to make/sell wiring kits, I do think that many of our electrical problems are related to poor quality and insufficient wiring gauge size for our Volkswagens. From what he is saying on his site; he offers either 2 or 4 gauge wiring for the alternator harness, definitely a upgrade from stock.

https://www.google.com/search?q=vol...ome..69i57.10774j0j4&sourceid=chrome&ie=UTF-8

At about $150, the stock wiring harness isn't cheap and puts the cost of the innovative products in perspective and it is possible, the new stock replacement will end up failing again. He also offers; a couple of different heavier gauges of wire and one "high out" cable with a inline fuse.

Here is a install/review of the kit: http://forums.tdiclub.com/showthread.php?t=273859

Alternator Wiring Harness
Common failure often the cause of a battery light
VW part #: 1C0971349AG

https://www.ecstuning.com/b-genuine-volkswagen-audi-parts/alternator-wiring-harness/1c0971349ag/

As I have said; I have been researching the cost of materials to make my own cable and professional ends, connectors, insulation, crimping dies/presses, tools, etc. and I am still trying to figure out if it is cost effective. Then I got hit with a bunch of electrical related failures this summer! When the heat here in New Mexico went over 100 degree F; my blinker relay stopped working reliably and then my gas cap actuator motor did the same thing! When it rains it pours; I have been working on replacing and fixing those problems! LOL! It never ends! :)
 
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