Melted Battery Top Fuse Box

[GOLDUST_TDI]

Hey guys, I replaced my battery top fuse box about a month ago - now it's melting again!! Before I replace it with a new one, I want to find the root cause of this. The wire that's causing the most amperage is the black wire in the picture which is connected to the alternator. I doubt my alternator is toast - so what the hell? The little research I did says the alternator wire should be replaced with a copper one. It seems to be a common problem but no clear solution! Please haaaelp! Thanks..

Golf

2002 TDI Golf

 

[BobnOH]

Other than evaluating the condition of the large conductors involved, you want to clean the engine block ground strap (actually on top of the transmission) and maybe the grounds under the battery as well. Clean the battery and covers.
In a DC system, current always flows to ground, when it can't get there it seeks other paths like dirt, moisture, like that.

 

[phaser]

Common problem on the Mk4, and I experienced the same melting issue.

Scroll down to the Mk4 section in the link below, and read the causes for the fuse box melting.

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

I bought a complete Mk4 kit, and went with a double alternator cable (which was offered at the time), providing a second pathway back to the battery. Problem solved, and excellent upgrade.

Looks like now they offer a single heavy duty alternator cable.

General google TDI Club search on melted battery fuse boxes:

https://www.google.com/search?q=site%3Aforums.tdiclub.com&ie=utf-8&oe=utf-8#q=site:forums.tdiclub.com+melted+battery+fuse+box

.

 

[GOLDUST_TDI]

Sweet - which cable do you recommend? Double alternator cable or the single heavy duty? Or which one is cheaper? This is such a common problem VW should have warrantied it.

 

[steve6]

Mine looks like that as well, I put the cover back on and ignore it, haha

 

[Vince Waldon]

When you replaced the battery box the last time did you carefully sand all the spade lugs so they were shiny on both sides, replace any nuts that were discoloured, and tighten the nuts very very tight?

I ask because if you skipped any of those steps the last time you may be doing a battery fuse box in a few thousand miles... again.

The box is melting because of heat at the connection... the heat is caused by dirt, moisture, or corrosion that causes an increase, however slight, in the connection resistance.

Doubling the size of the alternator wire won't change the heat that's melting the fuse block....at the connection.

 

[Mavrick]

A new or second alternator power cable is not necessary unless the cable is melted or damaged. Clean all connections at the alternator, fuse box, engine and chassis grounds. If problem continues, could have an alternator issue.

 

[joep1234]

Also check the output of the alternator, grounds and battery connections.

 

[TTTravisYT]

Check out my take on a permanent solution for this very common issue!

MK4 VAG Fuse Box Meltdown—Permanent Fix for VW, Audi, SEAT & Škoda