Charred/Burnt Battery Fuse Box...?

[Mr_Accord]

*** I know this is the MK4 Section, but my problem relates more to the charging system on the 2.0L 8V engine that is found in most MK4's than the model of car ***

The charging system in my mothers 2004 New Beetle Cabriolet started acting up last week (dash lights going crazy, engine chugging). I ran a few tests with my voltage meter and everything pointed to the alternator. A buddy of mine who has an alternator rebuild shop tested it and the output was all over the place. So he was able to get me either the 90amp which it already had or the higher output one at 120amp for $20 bucks more and he claims it should work without any upgrades to the cars wiring. I bought the 120amp alternator and installed this evening. I hooked my multimeter to the battery and it had a charge of 12.65 volts...good to go. I started the car and the voltage immediately dropped to 12.14v

...charging system still not working. I tested the voltage between the ground post on the battery and positive connector at the alternator and it was fluctuating between 12.80 and 13.90volts at idle so the part is working and its a wiring/connection issue. I decided to start back and the battery and check all of my connectors again and I realized I forgot about the fuse box ontop of the battery box. I open it up and the thick black alternator wire and the surrounding fuse is a mixture of melted charred black plastic...[censored]?

Has this happened to anyone before? Did the old alternator cause this on its way out or could this be me adding the higher 120amp alternator instead of the 90amp one? I read on some other forums that it could also be the positive wire from the alternator and that it isn't of great quality?

 

[cmorr]

I just did a quick search and it seem that VW installed 90AMP alternators on automatics and 120 amp alternators on manual transmissions. I doubt the wiring harness is different.

The wire that melted appears to be your main ground wire, am guessing there is resistance somewhere and I would check the connection at the other end (block)

 

[OneEyeJack]

Could an intermittent open ground be your problem. When the ground is open the alternator is asked to put out is maximum amperage and that can cause a lot of damage.

 

[pcoxe]

Looks like the terminal was loose. The other end of the strap didn't get hot and the cable insulation is only melted near the terminal block. It's all centered on the stud.

 

[Roadkingnc]

High resistance = high temperature, have seen it many times on different vehicles

 

[JHZR2]

All good answers.

Id check everything, including chassis grounds... THere is likely a strap from the body to the engine.

I have not had this, but I had a charred segment in an alternator wire where the insulation had cracked and moisture got in.

Dirty connections can make for high resistance which can get hot. However high resistance doesnt flow a ton of current which seems to be the case here...

So Im thinking the intermittent short is the case.

 

[HerrStig]

The output of a n alternator is controlled by the charging system so long as everything is properly working and grounded. A "bigger" alternator won't produce any more current than the charging circuit "asks for". It's like being connected to the town water system instead of your basement pump, so long as the pressure stays the same you won't notice the difference. I suspect your STARTER may be drawing excessive current. That component ought to be tested.

 

[DuckRyder]

Originally Posted By: cmorr
...
The wire that melted appears to be your main ground wire, am guessing there is resistance somewhere and I would check the connection at the other end (block)


It appears to be connected to the positive terminal, I do not think it is a ground.

I agree it looks like it could have been loose.

 

[Smoky14]

If that one wire isn't awfully expensive I'd replace it. If it is too costly, remove all the terminals and clean them thoroughly and buff them super clean with emery paper/ sandpaper and reinstall them. There is high resistance there and it looks like it is at the terminal itself.
Since it is near the battery I suspect that fumes from the battery started the corrosion and the curent draw merely helped things along.
Smoky

 

[tnt31]

Originally Posted By: cmorr
I just did a quick search and it seem that VW installed 90AMP alternators on automatics and 120 amp alternators on manual transmissions. I doubt the wiring harness is different.


I think you may have it backwards or it may be different for different model years. Early last year I replaced the original alternator (at least I believe it to be the original) on my wife's 2001 New Bettle with the 2.0L manual 5 speed and it was a 90 amp that I removed from it. I replaced it with a 90 amp. I had considered a 120 amp but it was a Sunday and I could not source a 120 amp so I just went with the 90 amp and it has been fine since.

 

[tnt31]

Originally Posted By: Mr_Accord
*** I know this is the MK4 Section, but my problem relates more to the charging system on the 2.0L 8V engine that is found in most MK4's than the model of car ***

The charging system in my mothers 2004 New Beetle Cabriolet started acting up last week (dash lights going crazy, engine chugging). I ran a few tests with my voltage meter and everything pointed to the alternator. A buddy of mine who has an alternator rebuild shop tested it and the output was all over the place. So he was able to get me either the 90amp which it already had or the higher output one at 120amp for $20 bucks more and he claims it should work without any upgrades to the cars wiring. I bought the 120amp alternator and installed this evening. I hooked my multimeter to the battery and it had a charge of 12.65 volts...good to go. I started the car and the voltage immediately dropped to 12.14v

...charging system still not working. I tested the voltage between the ground post on the battery and positive connector at the alternator and it was fluctuating between 12.80 and 13.90volts at idle so the part is working and its a wiring/connection issue. I decided to start back and the battery and check all of my connectors again and I realized I forgot about the fuse box ontop of the battery box. I open it up and the thick black alternator wire and the surrounding fuse is a mixture of melted charred black plastic...[censored]?

Has this happened to anyone before? Did the old alternator cause this on its way out or could this be me adding the higher 120amp alternator instead of the 90amp one? I read on some other forums that it could also be the positive wire from the alternator and that it isn't of great quality?

I have seen this problem on one of the VW forums I checkout from time to time. It would either be www.newbettle.org or www.vwvortex.com. Check those out and post over there to see if they can offer you some more help.

 

[pcoxe]

It doesn't have to be high current or high resistance. One of the formulas for power is current squared times the resistance(I2R). Just a half ohm of resistance at a modest 10 amp current is 10x10x.5=50 watts. Try holding on to a 50 watt light bulb for a few minutes.

 

[JimPghPA]

We and or You need to see an electrical schematic of where this terminal is in the electric system of that car to really understand what is going on here.

Is there any manual where you can get a electrical schematic so you or someone else can figure out where in the cars electrical system this terminal is located, how much current flows through that section, and what a poor connection will cause.

 

[HerrStig]

I would suspect the 120 amp alternator would be for the auto, which may have a good number of electronic components in it.

 

[scurvy]

Fairly common on mk4 VWs.

Disconnect the battery, then take both cables of a fuse holder off. Clean & reattach the cables. DeOxit isn't a bad idea here. Repeat for all of them.

Cleaning all the ground connection is also an excellent idea. I believe there are at least 2 in the engine bay. One may be under the battery.

120 amp alternators are often swapped in place of 90 amp ones for VWs with no ill effect, but no real benefit unless you've installed some other power-hungry devices (like a bangin' stereo). If you have the Bosch or Valeo alternator, the voltage regulator is a replaceable part; not so if you have a Hitachi unit.

 

[asand1]

Working at the VW/Audi dealer as a tech, I saw this all the time. Bad connection at the fuse causes excessive heat and then poof, melted. I would bypass that with a direct wire and inline fuse.

 

[Mr_Accord]

Originally Posted By: cmorr
I just did a quick search and it seem that VW installed 90AMP alternators on automatics and 120 amp alternators on manual transmissions. I doubt the wiring harness is different.

The wire that melted appears to be your main ground wire, am guessing there is resistance somewhere and I would check the connection at the other end (block)


Its not the ground, its the positive wire coming off the back of the alternator and going through a fuse box then on wards to the positive terminal.

 

[Mr_Accord]

Originally Posted By: pcoxe
Looks like the terminal was loose. The other end of the strap didn't get hot and the cable insulation is only melted near the terminal block. It's all centered on the stud.


I checked it and it wasn't loose, but it does have a lot of corrosion surrounding it.

 

[Mr_Accord]

Originally Posted By: Roadkingnc
High resistance = high temperature, have seen it many times on different vehicles


I was thinking of just going to my autoparts store and buying a few feet of 2 gauge and replacing the whole thing just to be sure. Is 2 Gauge suitable for a 120amps??

 

[Mr_Accord]

Originally Posted By: scurvy
Fairly common on mk4 VWs.


Originally Posted By: asand1
Working at the VW/Audi dealer as a tech, I saw this all the time. Bad connection at the fuse causes excessive heat and then poof, melted. I would bypass that with a direct wire and inline fuse.


I've been visiting the vwvortex forums and this seems to be a common occurrence on all mk4's