Hi all,

Recently picked upa mk1 vrs, just starting to notice small problems which need fixing (as expected with any car of this vintage!)

I see this has been raised a few times on here, but I had a fuse and holder (atop battery) replaced due to the plastic melting severely and causing a short and all sorts of dashboard lights on/off.

Within a day I notice some scorching and melting of the new holder around the left-most cable and connector.

I have read that a bad connection can cause this (nut is perfectly tight) or that replacing the alternator harness can cure the problem.

My query is can the contacts simply be dressed/cleaned to provide a better contact and resolve the issue.

Just wanted to know before handing over more ££'s.

cheers in advance

Hi Openwindow & welcome to briskoda.

What worries me with your problem is that you're not getting to the root of the problem!

A fuse should blow before cables or holders start to melt so maybe the fuse isn't rated low enough and the cable or holder isn't rated high enough either.

Do you know what the fuse is protecting?

Is it some after market add-on and thats gone faulty?

A bad connection will also cause problems so do that as a matter of course but don't ignore the other things.

It is quite common though....

Welcome

Thanks for the response and welcome John and vRSLen.

Unfortunately I do not know what the fuse is protecting, had the car less than a week so still finding my way around! I believe it may be linked ot the alternator - what highlighted the issue was the battery/alternator warning light appearing.

It is rated 110A and is one of 5(?) inside the battery-top fuse box (also houses 3 green fuses).

The car is completely standard and all electrics are working.

As it seems to be fairly common problem, I just wondered if there is also a common cure.

I must admit I was suspiscious about replacing a melted holder i.e. root cause which will ultimately melt the replacement!

Hopefully the added info will get a better response now.

110A is into the realms of welding current :S

The 110 amp is a link fuse. I would clean them up TBH.

borris, your post did not work, have another ago, and welcome

I think that the original alternator wiring loom is not quite up to the job. I replaced the one on my TDI and the cable on the new one was quite a bit thicker than the one I took off.

Perhaps as the batteries on the cars get older and the alternator has to supply more current for longer the cables start to overheat?

Hi,

There can be parts of a car electrical system that are not fused, for example: the main positive from the battery to the starter motor and the main positive from the alternator to the battery/starter motor. The fault you have has been mentioned elsewhere on here and is a problem, and my car has also had it.

The passing of current through a resistance causes heat. You will have a resistance where the cable bolts to the fuse if it is loose, dirty, corroded, mishapen; you can usually remedy most of these with careful cleaning and correct torque settings ("Test fuses for final torque; tightening torque 6Nm")

The job sheet I have says "Fuse for the battery has melted, replace the alternator lead and battery fuse box"

1J0971349FQ Harness £27.97

N10424906 Fuse £1.83

Labour £49.50

Hope that helps you

smile

A fuse should blow before cables or holders start to melt so maybe the fuse isn't rated low enough and the cable or holder isn't rated high enough either.

The fuse will blow if too much current is drawn through it. In the case of this problem the alternator cable has a too high resistance in the crimped connection before the fuse, so the current is not going through the fuse and enough heat builds up before the fuse to melt the fuse box.

The problem has been discussed here (and other VAG forums) many times.

The conclusion is that the termination of the cable goes high resistance and so heats up.

The only cure is to replace the cable, as well as the damaged parts.

With around 100A in the alternator cable (depending on model), it does not need much corrosion inside the termination (the bit you can't see) to produce the heat that melts the plastic.

See post by SMILEONIMPACT for part numbers.

Mike

Hi,

Fully agree with Pikpilot, with this fault the only option is to replace the cable.

On a technical note, the heat generated by resistance is calculated by the formula "Amps squared X resistance" therefore a resistance of 1ohm at the crimp with 20amps of current draw would generate 20x20x1 = 400 watts of heat to dissipate! Bearing in mind 20 amps is pretty low if your alternator is charging your battery, running all your lights, heated rear screen etc.. 60 amps is probably more sensible so triple the current in the formula and you have 3.6KW, more powerful than a 3 bar electric fire!

Smile

Many thanks for all the reponses to this, good to come across such an active forum .

It would seem a new cable is the best option, especially given the cost.

Thanks for the part numbers too, that was going to be my next question!

Take a look at this one. Never travel in a taxi.

http://www.ilexa.co.uk/forum/index.php/topic,22980.0.html