Melted fuse block on battery - S177

Today was pretty hot and it seemed to take a little while for the A/C to get cold, so I decided to check the radiator fans when I got home. Good thing I did, since I found this:



So apparently that's fuse S177, 150A on the wire to the alternator. I guess this could happen just due to corrosion or a poor connection, but could it be indicative of an alternator problem? The black wire was hot even several inches away from the connector (which was off course too hot to touch), and the red wire next to it was pretty warm also but not as bad.

Battery voltage seems normal, maybe slightly low. 12.40V key off; 12.21 key on, running VCDS scan (no codes). Hooked up a battery charger which showed it at 75% charge and fully charged it in about 10 minutes (10A charge rate). 12.56V after letting it sit 15 minutes (disconnected from charger, still connected to car).

Started engine, voltage at battery posts was 13.31V. Definitely low, but maybe caused by the high-resistance connection; unfortunately I forgot to check voltage at the alternator itself. After running just 90 seconds, the connection at the fuse block was very hot and I smelled melting plastic, so it's not drivable like this.

Obviously I need to replace the fuse block, and probably the cable too, since even if I shine up the connector, the crimp doesn't look so good any more. I took out the alternator and am going to have it bench-tested. I hope the alternator is good, but on the other hand, having this happen with a "good" alternator isn't so great either.

(Oh, and the radiator fans are working properly.)

I had the same issue early last year, and replaced the fuse block, lid and the battery cables.

These battery cables in the kit are super heavy duty, and worth every penny.

http://innovativewiring.com/?page_id=161

And see this thread:

https://forums.tdiclub.com/showthread.php?p=4271815

.

phaser said:

I had the same issue early last year, and replaced the fuse block, lid and the battery cables.

These battery cables in the kit are super heavy duty, and worth every penny.

http://innovativewiring.com/?page_id=161

And see this thread:

https://forums.tdiclub.com/showthread.php?p=4271815

.

Click to expand...

Just had this problem on my 03' alt. cable was so hot it lifted the fuse connection up. I went to junkyard grab a good fuse panel and cut off that steel lug and install a good copper lug and u will be good to go. My volts where low like yours and after the fix i got great volts now with a/c on 13.9-14.1. Use to be 13.1-13.8. Also Car seems to ran alittle better too.

The alternator itself is probably fine. Although I've not experienced this issue (yet), myself... I have seen this mentioned on the forum several times. It is most often attributed to corrosion in the wiring or loosening of the 10mm nuts that hold the fusible links (resulting in higher resistance connection, which in turn gets hot when current passes through it). I loosen and re-tighten the 10mm nuts on my car once a year or so. Come to think of it, I haven't done that lately....

Had this problem too but noticed it before melt anything. The fix was re-tight the crimp and solder it to avoid future incidents.

phaser said:

I had the same issue early last year, and replaced the fuse block, lid and the battery cables.

These battery cables in the kit are super heavy duty, and worth every penny.

http://innovativewiring.com/?page_id=161

And see this thread:

https://forums.tdiclub.com/showthread.php?p=4271815

.

Click to expand...

I had read that thread last year and mentally filed it away as a "maybe, someday" upgrade. Well, that day is today, since I can upgrade the whole battery/alternator harness for the same price as just the single alternator cable from the dealer. Ordered the "standard" harness since I don't care for the "base" piggybacking the alternator off the starter without a fuse. Thanks for reminding me of this option!

Also bought a fuse box on eBay (used, genuine VW). Reviews of some aftermarket versions said they didn't fit well or snap into the holder properly, so I figured I'd stick with the real thing but at 1/3 the new cost. I will of course polish the connections and apply terminal grease after assembly.

had same problem on wifes car.. left her standed as the alternator would not charge through it... cleaned it, but finally had to replaced connection on the black cable and problem never came back.

The same terminal smoked and slightly deformed on my car. It was cranking slowly. Turned out I needed a starter. Replaced that and all was. Well for 4 months or so. This past Wednesday My car wouldn't start. I got a jump and went to ORielys. They diagnosed battery. Installed new battery. Ran it for a day, then again, no start. Got another jump and went back to OReilys. They said the alternator was only making 9 volts. Before, the battery lite was not on. Now it was. Installed new alternator. Battery lite still on. Disconnected battery and checked continuity across the first fusible link on left side of fuse block. No continuity. With engine on, jumped the fusible link, and battery lite. Went out. Cleaned up the connection and all is working fine.

Same problem with my ex's GTI. further inspection revealed the PO of her car had soldered the flat fuse together after it blew instead of paying like $2 for a new one. Replaced the fuse and cleaned up any corrosion and was no longer an issue.

Best thing to treat the contact area for the fusible links is an aluminum electrical contact paste. It's anti-corrosive and keeps the contacts nice and clean .

Also, check the operating voltage your alternator and condition of the battery cells. I much prefer a battery that you can unscrew the caps to the cells and check the charge directly to each battery cell. Just last week, we found a dead #1 cell in a customer's car. We didn't have a replacement battery on hand, so we suggested one from a local company in his home town nearby. The next day after installing the new battery, he had a dead battery! The fusable link was melted out in the same spot as yours.

What we figured out is the parts jockey at the auto store replaced the battery and never looked to see that between the time the owner left my place and drove the 25 miles to the auto store, the fuse melted out.

Not only corrosion will do in the fusable link. Obviously a bad battery or overcharging circuit will do the same. If you read voltage across your battery with the engine off, it should read around 12v, +/- .5. With the engine running and the battery charged, it should read 13v-13.5v. If the charge reads high (14V+), either the battery is causing excess load on the alternator, or the alternator's regulator is going bad.

We find it important to check the specific gravity of the battery acid. That will guarantee battery quality. If the battery won't take a full charge, it will strain the alternator. So, checking battery charge, cell to cell, will help you know when a battery is bad and that will keep you from what we see too often... we replace the battery, only to find the alternator worked itself to death on a bad battery. Batteries are cheaper than alternators. A battery that will take a good charge keeps the alternator living for a longer time. It will also keep you from melting out a fusible link.

I'd check your battery.

part number

Does anyone know the part number for that fuse block? Was checking mine today and it's toast need to replace it. The bolt won't even sit straight in the pocket.

The alternator wiring harness needs to be replaced. Corrosion wicks itself under the insulation on the large fat wire from the alt output to the fuseblock. This is the area where all of the heat his being generated (was too hot to touch several inches back from the fuseblock). This fat wire in the alt harness needs to be replaced. The melted fuseblock ends up being collateral damage from the fat wire getting hot and should also be replaced.

An easy test to do is run the car with a heavy electrical load on the system (all lights on, a/c on, hvac fan at highest speed, rear defrost on) and measure the voltage at the battery. Then measure the voltage at the ALTERNATOR output terminal where the fat wire in the alternator harness connects. The alternator output will be around 14V and you'll probably find the battery voltage to be around 12.8V. That means you're dropping 1.2V across the alternator harness wire! The majority of the voltage drop will be in the last several inches of the fat alt wire right where it connects to the fuseblock. That's where all the heat is being produced due to the wire's added resistance due to the corrosion. With a good alt harness wire, the voltage drop between the alternator output terminal and the fuseblock on the battery will be negligible and the battery will be at about the same voltage as the alternator output.

I've been through this before with my 05 ATD PD JWagen TDI a few years ago (recently sold it to mrchill a few months ago).

Good luck.

I replaced the harness a few months ago, but forgot to follow up here.

former chevy man said:

Does anyone know the part number for that fuse block? Was checking mine today and it's toast need to replace it. The bolt won't even sit straight in the pocket.

Click to expand...

The only part number on mine is 1J0 937 550 AB; I read that this part no. only refers to the lid and there's a different number for the bottom, but you'll frequently find people selling the whole thing on eBay under that number. Also try searching without the AB suffix; apparently 1J0 937 617D is also another part number for this.

Amazon reviews indicated some aftermarket parts don't fit quite right, so I bought a used OEM part off eBay and it works great. The only variations among OEM parts is whether there's a 110A or 150A fuse on the alternator cable. My 150A fuse was trashed (but not blown, somehow!), so I made sure to order one with a 150A fuse.

I also installed the Innovative Wiring harness at the same time. A bit of a pain to bend the thick wires into place, but not too bad. Also, on the PD there are no empty 6mm holes on the cylinder head for the extra ground wire in this harness, so I ended up using a bolt on the coolant flange. Bonus: it now turns over much more quickly when starting! Now I have the same 14.5V at the alternator and at the battery (14.29V according to VCDS).

My only complaint is the battery terminal bolts are harder to reach than the OEM terminals (the bolts point to the side now), and they're in Imperial sizes. The only thing that fits on the positive terminal is a 1/2" box wrench -- there's no room for a socket or an open-end wrench.