blown hu amp cause smoke, melted wires?

A few preliminaries Me: I'm new to do-it-yourself stuff and try to take a cautious and well informed approach before trying anything myself. I'm a civil engineer, not electrical, though. I did quite a bit of research, especially on another forum geared towards my particular car. The car: 1999 Passat B5 GLS 2.8L V6 30 valve, 5 Speed Manual Satin Silver with Black Leather Interior The stereo: Kenwood Excelon KDC-X591 Stock speakers No amps or other equipment except a Simpletech 160 GB portable hard drive is connected to the HU and is located in the glovebox. Because the HU only provides a single USB output with 0.5 mA and the HD needs 1 A, I needed to install a switched 12v outlet. I decided to install it in the glovebox. I use a USB adapter plug in the new 12v outlet and provide the missing 0.5 A through the secondary plug on the provided cable. The Problem: Since the install, everything had been working great for a 3-4 months. Then a couple weeks ago I was on a leisurely drive with the wife and kid when I hit bump or chuck hole. Almost immediately thereafter, the stereo cut out and a few seconds later my wife noted that smoke was coming out from under the dash on the driver's side below the steering wheel. Later, I traced the problem back to wiring behind the stereo head unit. Assuming I had botched the job, I inspected all the wiring I had done and found that all of it is still intact and looking good. Surprisingly and somewhat baffling, the problem appears to have occurred with the wires on the factory side of the harness, which look like they overheated and melted! Following is a schematic of the situation: Factory Wire Bundle-----X-=]------<>----Aftermarket HU where ---- are wires = factory plugs ] after market wiring harness <> soldered connections I made between harness wires and HU wires X location of melted wires To clarify, some of the wires at the back of the factory "plugs" that snap in to the back of the stock head unit melted right next to said plugs. From the aftermarket wiring harness to the head unit's bundle of wires, all that still looks good. I also checked the wiring I did for the 12v plug I installed in the glovebox which ran to a switched lug under the steering column--it also looks good. I checked all the fuses I could find--even those I could get to under the dash (not knowing any better). HU fuse ok. They all seem ok. I had been using the stereo and 12V recepticle for quite a while on a daily basis now. I routinely had it cranked up to nearly the max. (In my car, while driving, that's not terribly loud for whatever reason. Especialy on older 80's music.) But on the day it smoked, I had it down to a low volume level because I had my wife and kid in the car. On one occasion weeks prior, in the middle of my 30 min commute home from work, while listening to tunes with the volume cranked nearly to the max the sound kind of got distorted and faded out. I turned it down and then after a while brought it back up and it seemed fine. Perhaps this should have been a first clue to suspect something...but I just thought it was the HU getting overworked. In the mean time, I've completely disconnected the HU (although it is still in its place in the dash) and the HD. Over the past two weeks the car seems to be running fine otherwise. Am I safe to keep driving the car or should I take other electrical precautions? Long term, I really can't stand to drive without my stereo...but I don't just want to rewire and reinstall without knowing what caused the problem. Could it have something to do with the wire gauge? I noticed that the factory wires seem a bit thinner and flimsier than the new wires. Shouldn't a fuse have blown somewhere to have prevented the wires from melting? Any ideas as to what caused the problem and how best to confirm it? I really want to know and understand what the problem was before I try any repairs. Thanks in advance, for any advice.

What was the impedance of the factory speakers?  If they are 2-ohm speakers you might have damaged the HU amplifier (which might be the cause of the fade out) and perhaps - although this is very unlikely - the reason the wires smoked was over power?  Or maybe they got damaged during your installation and you simply didn't notice.  In any case, can you tell which wires smoked - power, speakers, something else?Support the12volt.com

You only show one wire. Is that all that smoked? Was it a power wire? A ground? What color was it, so we can possibly help in identifying it. (If you can't tell exactly what color it is, what color wire did it connect to in the harness adapter?) When was the last time you had the car waxed? (OK, that's just a silly question...)It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

(Click here to view a larger image.)  I've unplugged the black one of the two stock plugs (the other being brown) from the aftermarket harness to afford a view of the melted wire. The brown plug (still inserted in aftermarket harness and not visible in photo) and the black plug originally snapped into the back of the factory HU. This was as far as I could pull out the stock wiring. It looks like only one wire melted. Can anyone tell what the melted wire was to/for?

(Click here to view a larger image.)  This shows the wiring that I installed. The two stock plugs (one brown, one black) plug into the aftermarket harness. I soldered the wires on the aftermarket harness to the wires from the aftermarket HU. The wiring still looks good (no melting, at least).

My install, when it was finished.  Thanks for any help that will get me back to listening to tunes while driving!

Looks like with the first photo it's Pin 3 of your power harness which on a 99 passat, is going to be your switched +12v accessory.

KPierson wrote: What color is the wire in the radio harness that lines up with the burnt wire?  Aftermarket wiring colors are all the same, stock colors are different so it would be much easier to figure out what wire it is if we knew the aftermarket wire color.  From the looks of it it appears to be the power harness, but I only say that because of the thick wires.  How do the pins look in the harness?  A loose connection can cause wires to heat up and melt without blowing fuses.

I will double check and confirm by pulling the HU this evening, but it does look like it's the switched power wire. 

What am I looking for when I inspect the plugs and harness for loose connections.  Is it as simple as tugging on a wire and if it comes out then it's a bad connection or is there more to it? How can I fix any other loose connections?

If there was a loose connection on the factory plug or new aftermarket harness, and that is what caused the meltdown, is it possible the HU is still ok?  Where can I go to get the HU checked or is this something I can do as a do-it-yourselfer?

Thanks for the help so far!