I'm sure everyone knows the heat in the southwest is a bear, I am an auto electrician one of two auto electric shops my comp will not touch VWs so when these started showing up at my shop i first noticed the fuses had not popped so it was not too much current, what i did and worked permanently was just used a bus bar and housed it the bolts on the buss are longer and have more contact area, i have not had one come back, not too many techs know electrical for it takes more thinking than just doing mechanical, but ya the longer bolts will work periodThe fusebox on my 1.8L T new beetle recently melted and warranted a further look. This issue appears to be pretty common among this and other similar VW's so I've decided to share my findings and what I feel will be a long term solution.
I agree, the problem is excessive heat at the connection interface between the wire terminals and the fuse, not excessive current in the wire (remember the fuse didn't blow and the entire wire isn’t melted). I believe that the root of the problem is that the connection on the non-battery side of the high current (i.e. alternator and interior) fuse loosens slightly over time. This creates increased resistance, which tends to soften the black plastic housing base, reducing clamping pressure which causes even less contact, more resistance and more heat until everything spirals out of control. Poor design from the get go.
The battery side of each of the fuses tightens up with nuts that are all metal-to-metal clamping everything together and remain tight over time. This side never gets hot and never has a problem. The non-battery side of the fuses (towards the rear of the car) is different because they are all individual. Each individual bolt comes up from the bottom, and comes thru holes on the black plastic housing. There is a thin drawn sheet metal washer that is supposed to support the clamp load of the tightened nut. The problem is that this sheet metal washer is totally inadequate to support the clamp load and crushes easily under the clamp load of a tightened nut. (Clamp loads on a tightened M6 nut can be hundreds of pounds) A better design would have been to use a metal screw with a shoulder washer with some thickness that wouldn’t deform under load. I’ve looked at several different manufactures fuse blocks including Genuine VW parts and they all share the same poor design.
Here is what I did to solve the problem. Get a new fuse block. Remove the bottom black plastic flap to expose the back of all of the hex screw heads. You’ll need a small screwdriver to open all the snaps. All of the 10 M6 bolts will need to be increased in length on both sides of the fuse. I left the thin drawn sheet metal washers in place, but added an additional nut on the topside of the plastic so that the fuse now bottoms on the new nuts above the black plastic rather then crushing the drawn sheet metal washers. I used some Loctite on this nut and let it dry before final assembly. You’ll need to add a nut to both sides of the fuse to lift up both sides so that the fuse stays horizontal and isn’t cocked at an angle. The basic idea is that when the nuts are tightened up the top outside nuts clamp the fuses to the wire crimp terminals and then bottom on a new Loctited nuts instead of the flimsy sheet metal washers. All stresses remain in the metal, bolts/nuts/fuses and terminal ends and there’s no load clamping the sheet metal washer or the black plastic base. The nuts will stay tight, Consider adding a split washer in the stack-up to retain clamp pressure.
Pay attention to get the correct size fuses back onto to the correct wires! Different years and models use different fuse values.
Remember when you put the bolts back in they need to be rotationally aligned to fit into their black plastic hex receptacle in order be able to shut everything back together. Pay attention to this otherwise you will go thru multiple assembly cycles like me.
There’s no need to over tighten the nuts. They wont come loose over time. Overtorquing will just spin the hex head in the hex of the plastic base and ruin it making the base hard to close.
To verify everything’s working well once you start the car back up and the alternator is charging the battery with max current, the top of the rear bolt on the fuse block should remain pretty cool to the touch. If it’s too warm there will be a voltage drop between to B+ side of the fuse (front of car) and the eyelet terminal of the alternator wire. Even a .1-volt drop at this junction with 80 amps of charging current will generate 8 watts of heat in a very tiny area. The lower the voltage drops, the cooler and better! Check it over time until you are sure everything is steady state.
As for the three 30 amp flat bade fuses, I’ve also had the same problem with intermittent AC fans and or ABS brakes due too poor electrical contact. My diagnosis is similar. Its not excess current but poor connections caused but cheap terminals that cant support the current loads.
To solve the problem at one point, I out boarded a 30 amp Air Con fan fuse (got my solder iron out), which worked but wasn’t pretty. In my most recent iteration with a new start over fuse block I noted that the sheet metal fingers which contact the 3 fuses were rotated 90 degrees giving substantially better metal contact area with the fuse terminals and so I added silicone grease to the fuse blades and kept the aftermarket manufactures rotated design. If you have the original design (contacts all in the same plane) I suppose I would outboard all three fuses. Not pretty and a lot of soldering work. Make sure you use fuse holders (Amazon has 30 amp fuse holders) which can support the 30 amps…….Volkswagen didn’t. If they did ,we wouldn’t have the problem and there wouldn’t have been class action lawsuits.
(I don’t think you can determine which design you have unless you take it apart)
Good luck, hope my pictures help
Cheap sheet metal stamped washer, which is sandwich thru the black plastic base.
This is the root of the problem because it gets crushed.
This is basically my fix to add nuts to the top of the sheet metal part. Note Loctite.
Nuts were also added to the battery (front) side to allow the fuses to remain horizontal.
All bolts were exchanged for longer pieces to allow for the extra nuts.
The bolt hex heads need to be rotationally aligned to fit back in their respective plastic recess’ allowing re-snapping everything back together.
30 Amp Fuses
My original fuse block I had to outboard the AC fan fuse because of poor contact. Note the orientation of the tangs contacting the fuse blades are all in the same flat plane. It’s a Poor design with minimal metal contact to the fuse blades, hence the need to outboard the fuse.
Once I had the alternator fuse over-heating issues, I decided to start over with a new fuse block (modified as shown above), which happened to have improved 30 amp discrete fuse holder contacts. This design looked much better with more surface area of metal contact so I decided to keep it with no modifications, except to add silicone grease, however I do periodically do the same voltage drop test I did above. Remember voltage drops generate heat, causing melt down.