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2004 VW Jetta TDI BEW
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Discussion Starter · #1 ·
Ok after many days of troubleshooting, testing pins, the alternator, the battery fuse panel, and the fan control module, we think our next step is to replace the alternator harness. My husband is thinking of building this harness himself but doesn't know how exactly it is put together inside. Since this is our only vehicle we want to get as much info first as possible before taking the old harness out and rendering our vehicle out of commission. What he and I are wanting to know is do those small wires with the plugs connect into the main big wire that runs from the alternator or are they separate inside? that big bundle? The pic is of the harness we would need should we have to buy the actual thing and not make it ourselves.
67230
 

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Mk4 VR6, Mk2 16v, E30, P71 CVPI
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The small wire is for turning the alternator on, monitoring charging voltage, and triggering the battery/charging warning lamp. It just runs alongside the large charging cable, doesn't interact with it in any way. Here is a example of cables I made using the parts I was talking about in your other thread. This was for a 1992 Jetta that only had a single control wire to the alternator. What you'll see is that I pulled the old cable out and transferred the stock small wire to my new charging cable, which it what you would want to be doing. I wish it was a clearer picture.

 

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Discussion Starter · #3 ·
The small wire is for turning the alternator on, monitoring charging voltage, and triggering the battery/charging warning lamp. It just runs alongside the large charging cable, doesn't interact with it in any way. Here is a example of cables I made using the parts I was talking about in your other thread. This was for a 1992 Jetta that only had a single control wire to the alternator. What you'll see is that I pulled the old cable out and transferred the stock small wire to my new charging cable, which it what you would want to be doing. I wish it was a clearer picture.

Ok 😊 thanks!
 

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I agree with the above, the parts look as good as anything I would make. It seems a little pricey, but I'll attach a picture I just took of a ground cable that cost about $25 in materials, only because I had had them all lying around. Then there is the crimping tool, the cable cutting pliers, the strippers, the heat gun, the experience. I would never tell somebody not to try a new craft out of desire, but it seems like it makes sense to buy rather than make in this case.

 

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Discussion Starter · #8 ·
Auto zone carries them I think... it's just a large lengthy wire and proper insulations with two .... crimped terminals.
Ok, I'll check there, we did end up ordering a new fuse box that goes on top of the battery, it is supposed to be here on the 12th. My husband is confident he can make it himself to get by he ran a separate cable from the alternator to the battery and that has kept the other wires from getting hot and has kept our voltage where it needs to be. Ultimately though we want to replace all of them.
 

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It's fine you can make it yourself, those are #2 or later wires I think, but the insulation is not the same as the HomeDepot home electrical wires ... Welding wires would be OK... the lugs they sell in any auto store dependents on the wire size you choose... ..

as far as the fuse box, you can transfer the fuse over if the one you have is better quality... for me. My new one was a $20 ebay one box is the same, I transfer the fuse over, added di-electric grease to slow the corrosion, It's been 4 years and I did say it's working.
wire brush all the other terminals when you are there... yea that fuse box is one of the PITA problem that VW won't acknowledge. Just google the burned VW MKIV fuse box...


I have seen your fusebox pic from the other thread I think, wasn't that bad at all.. just the lugs are a bit darken grey from the left of the pic the first cable looks bad (it's the alternator cable) the third one also looks bad. Not sure if it is the shadow, dirt or the camera, it shouldn't be black... usually if it is really problematic, you'll see green or lots of grey on the lugs and the first 1" or so of the terminals will be discolored.. Normal copper is golden/bright copper look not dark grey/green or any other dicolorations.

You probably won't be able to replace all of those wires that connected to that fuse box.. might have to look for a way to see how you can correct the first 1" of that corrosion problem... AGM battery helps.. since it doesn't give off battery fumes. Any who..
 

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Discussion Starter · #10 ·
It's fine you can make it yourself, those are #2 or later wires I think, but the insulation is not the same as the HomeDepot home electrical wires ... Welding wires would be OK... the lugs they sell in any auto store dependents on the wire size you choose... ..

as far as the fuse box, you can transfer the fuse over if the one you have is better quality... for me. My new one was a $20 ebay one box is the same, I transfer the fuse over, added di-electric grease to slow the corrosion, It's been 4 years and I did say it's working.
wire brush all the other terminals when you are there... yea that fuse box is one of the PITA problem that VW won't acknowledge. Just google the burned VW MKIV fuse box...


I have seen your fusebox pic from the other thread I think, wasn't that bad at all.. just the lugs are a bit darken grey from the left of the pic the first cable looks bad (it's the alternator cable) the third one also looks bad. Not sure if it is the shadow, dirt or the camera, it shouldn't be black... usually if it is really problematic, you'll see green or lots of grey on the lugs and the first 1" or so of the terminals will be discolored.. Normal copper is golden/bright copper look not dark grey/green or any other dicolorations.

You probably won't be able to replace all of those wires that connected to that fuse box.. might have to look for a way to see how you can correct the first 1" of that corrosion problem... AGM battery helps.. since it doesn't give off battery fumes. Any who..
Ya, we got the new box just more of a precaution than anything. As far as I know, he is planning on ordering specific cables that are copper and are 2 gauge for the main wire, and 4 gauge for the rest including the wire going from the fuse box to the battery. We have gotten these cables from eBay in the past for our 86 suburban that is used as our snow plow, and those have been great. They sell it by the foot red or black and can have ends soldered, crimped, and heat shrinked on. They have been amazing on our old plow. I can give you a link to them if you are interested.
 

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Thanks, I am good, I make my own cables, but since you mentioned, I just throw that caution out there that your husband don't go out the HomeDepot and get the wrong types..Home electrical cables are different in stiffness and insulation, even thought it's the same gauge wires..
 

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Discussion Starter · #12 ·
Thanks, I am good, I make my own cables, but since you mentioned, I just throw that caution out there that your husband don't go out the HomeDepot and get the wrong types..Home electrical cables are different in stiffness and insulation, even thought it's the same gauge wires..
Right, ya we knew that home electrical wires are different than what is used on auto.
 

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Ok, I'll check there, we did end up ordering a new fuse box that goes on top of the battery, it is supposed to be here on the 12th. My husband is confident he can make it himself to get by he ran a separate cable from the alternator to the battery and that has kept the other wires from getting hot and has kept our voltage where it needs to be. Ultimately though we want to replace all of them.
4 awg stranded copper cable, gold plated terminals, adhesive filled heat shrink, and most importantly a hammer style crimper. You cannot crimp 4 awg by hand properly. I have done many battery relocations, upgrades and alternator upgrades :) happy to help
 
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