I have a 2001 VW Beetle which has a nasty habit of melting the above battery high voltage fuse box. I've replaced it three times already and replaced the alternator as well, but I'm at a complete loss as to what's causing the problem.
Apparently this is a known issue with VW's from that era, there's even a class action suit against VW that's still working its way through the courts.
Is there a real, permanent solution to this problem?
As I understand it, there was a fundamental redesign in the cars from around 2002 onwards. Unfortunately that doesn't help you but I wonder if it is possible to retrofit the later model fuse box.
Thank you for the picture, this has cleared things up. The fuse that has melted in your unit is S177 which is wired to the alternator. Apparently as the cable which goes from this fuse to the alternator gets old it begins to corrode, resistance increases as does the temperatures.
The tried and tested solution amongst the VW guys and gals seems to be to replace this cable with some new, heavy duty shrouded cable to bring the resistance (and associated temperature) back down. The cable runs from this box down through the battery tray, around the back of your inlet manifold and to your alternator. Make sure you disconnect the battery before changing this cable and if in doubt, seek assistance from an auto-electrician.
I had to deal with this problem some years ago on a VW. What I noticed is that the fusible link ran slack, causing the connection to arc and as a result burnt out the plastic housing below. I couldn't get a fuse box so I by passed the burnt area, had a link fabricated and secured it with a bolt and nut.
Replace the wire between the alternator and the fuse box.
It's called the alternator harness, but I haven't found it for sale online. It is just a simple (large) wire with two ring connectors crimped on the ends.
It tends to get a break in the wire near the fuse box that then arcs and overheats; this is not a problem with a short otherwise the fuse would blow, this is an arc.
I have a 2005 Golf MKIV and it did this also. Lost a/c, fans, overheated. The B+ wire from the alternator to the battery appears to be too small a gauge. I went to a larger gauge wire and replaced the fuse block on top of the battery. It also appears that the contacts for the three green fuses are not to tight fitting. My wife's a/c went out again last week. I moved the fuse around in it's socket and the fans and a/c clutch would then go on and off. I pulled out the fuse to slightly warp the contacts for better contact and I got the ends of my finger blistered for my effort. There was also a black arc literally burnt into the fuse contact. So when you see a company marketing their fuse block as good as the original, you might want to question that. A very shabby condition for such a technologically advanced company. Just no conscience...ergo the TDIs of late, and this too. Very disappointing. This is the only problem we have had with this car in 11 years and 112,000 miles.
An overheated electrical connection has but one cause, resistance to electron flow. Find the cause of this and fix it. The test for this is voltage drop under load.
1) Repair first. Replace all the burned parts with new high quality units, including the wire to the alternator. All bolted connections are to be torqued to specification. Consider reinforcing crimped connections with solder. All connections are to be cleaned to bright metal. Stabilant 22 will be painted on the faces of the bolted connections. Ensure that the bolted connections are not subject to vibration that could loosen them over time. Consider adding tie downs for the wires near the fuse box if none exist. 2) Now test the circuit. This will determine if the electrical resistance is fixed or is still present. Using a high quality volt meter measure the voltage loss of the circuit from the battery side of the fuse to the alternator connection. During this test the engine will need to be running and the high power use vehicle electrical systems will be on, heater blower, headlight, rear window defrost, etc… This value needs to be less than 0.1 volts, but a high quality circuit will have less than 0.01 volts. If this value is low then repairs are complete, if not narrow the search by testing shorter sections of the circuit until the problem is located. 3) To ensure the repair over time test the circuit in the manner listed above as often as you like, as long as the voltage drop remains low the repairs are holding. If not test for and repair the connection with the elevated voltage drop.
The B+ wire is likely alright if you noticed it on time, but the problem is due to the drained battery and the bad connection around the fuse. If it was the wrong gauge or something, it wouldn't melt around the fuse but likely elsewhere or wouldn't provide enough current to cause any damage.
This happened to me on 2002 Beetle a week ago. After my alternator died, I, apparently, drove on battery till it died in turn and I had to be towed. Alternators are meant to maintain battery charge and not to charge a totally dead battery as it would draw a very high current that may damage the alternator and, yes, melt the fuse. I replaced the fuse box, sanded well all the contacts, replaced 110A fuse, and greased everything up while charging the removed battery by a dedicated battery charger. The ammeter on the charger was showing very high current for a first couple of hours.
While replacing $150 worth harness won't hurt, get a peace of mind and buy a battery charger to use next time alternator dies.
Replace the box. Get a 49" #4 battery cable from parts supply house. The wire will have eyelets on each end. Use one eyelet and remove the other. Replace the missing end with one with a smaller hole; I found one at tractor supply. Next remove part of the stock so the end will fit the new fuse box. The old cable is shot do not try to remove it just cut off the ends and as you follow it with the new wire use pull ties to secure. Be careful that you have all wires and plugs connected before turning on the switch. This mess is caused by bad wire ( VW & MB don't use the good stuff) then they went from a 90A to a 120A alt. with the same wire. This fix worked on my wife's 2006 tdi. Note: feel the wire if it is hot it is 1. overload 2.bad connection 3. bad wire.
