i thought i would keep this thread together by answering my own questions (i kept the original post below this one). essentially my rebuilt alternator was in my car for about an hour before it blew up and fried my wiring harness. most of you made the wise diagnosis that the alt had grounded to the frame somewhere and shorted out. i was worried i had just f'ed up the install or there was more electical problems with my car than i thought.however, just as you predicted, after i pulled it out this is what i found:


you can see that the washer on the rebuilt alternator is raised compared to the original equipment (this is the one i just put in my car...notice the b+ washer on the right is flush...this is very important!:

anyway, second time around was quite a bit quicker...i think it took me about 45 minutes to get the thing out. while i was already covered in dirt and grease i went ahead and did my first valve adjustment...car runs awesome now but the valves are a fair bit louder. i wonder if this is how they are supposed to sound being that they were just slightly off the mark (some of them not requiring any adjustment)? i did .004 in/ex
anyway, just wanted to reiterate what is explained in the classics thread, this is a serious problem and nobody i spoke with at pelican had any idea about it. oh well, seems to be working well now that i've got an OEM one back in the car...
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after some huffing and puffing, i got the alternator in and out after i fried the diodes from a foolish switching of the battery poles...
anyway, putting in the new alt and checking all the connections twice, i fired her up...
and the "g" light...went off!!!!
success i thought. i spent the rest of the weekend trying to get the heater and working properly.
anyway, drove the car for about an hour...stopped and started the car about 5 times. absolutely trouble free driving.
however, on my 6th start up after it had been sitting for maybe 10 minutes? a large amount of black smoke came out of the engine bay ...as soon as i saw it i cut off the car and checked for damage assuming it was some tubing from the heater which had caught fire touching the engine or something? i was wrong; it was the wire running from the alternator to the starter...in fact, it was still smoldering when i lifted the lid to the engine bay
this is what i found (this pic is taken after i put electrical tape on the bare wire:

took a look back at the starter...the burn went all the way to it:

here's the best shot i could get of the underside of the car:



so i'm thinking, how did this happen? did the wire touch the intake pipe and catch on fire? perhaps, here's a pic of some rubber on it...and it did do it when i started the engine, perhaps when the engine "shook" to life it was still hot and touched the wire igniting it..check the first pic as well...

so...i fried the wire...and when i started the car again...the F%$KING "g" light is back on!!!!! everything works perfectly though. car starts fine...all electrical works, no fuses are blown
so, what do you guys think? did i mess something else up in the electrical system or did this wire's insulation catch on fire, cause a short and did it fry my alternator once again?
can i buy new wires for the alternator?
i'm bummed, thought my days of alternator swapping were behind me...hopefully this was just a freak accident...and there isn't something more complicated wrong with the system...here's a pic of my relay...nothing looks out of the ordinary there...again, new VR

any advice is greatly appreciated. looks like i'm toolin' instead of driving next weekend

May have fried the alternator too.

There is a stud sticking out of the back of the alternator that is too long on the Bosch rebuilds and can short to a cover.

Do a search for particulars on that failure to see if that is what happened.

Ken

I feel your pain: I did the very same thing on my old 4 banger -- very spectacular as the alternator diodes exploded...and the wire to the starter burned. Talk about feeling stupid!

There's no fuse for that wire (why?) -- it was most likey burned through when you originally fried the alternator and you just finished the job "really good"

I think you're done (others may have a better idea)...replacing the starter wire should do it, but check the wire from the B+ terminal to the battery on the alternator too. I think mine looked supect and I replaced it, but it's so long ago I've forgotten (bad memory!)


Good luck!

Do a search. this is the common cause. I went through 3 alternators and that same wire, I actually got to watch it fry as my dad reconnected the battery. Jeff Bowslby sell replacements at a great price.
I ended up putting some gasket material between the alt cover and the diod to keep it from shorting.
Samson

hey,
thanks for the replies guys...ill try the search. but just to clarify; it's the back of these things that have an issue? the part opposite of the fan belt?
man, i felt like i read about this extensively on here and i never saw this mentioned...bummer
but, now i know

Hey...there again...I remember talking to you before with the "G" light issue and we suspected you blew a diode or had a bad regulator--one that would come out of the relay board if I remember correctly.

Perhaps the other guys are correct about the backing plate shorting out...but with your previous symptoms, I'm not to sure about that.

When I saw your relay board picture I noticed the yellow wire which made me think of my 1.8 motor with FI. Now I can see from your runners that you have carbs now but do you still have the double relay that is hidden below you battery box? If you do and it is still hooked-up it, it would be worth it to check the connections to it from the harness. Mine at one time had one of the spade connectors come loose and would intermittinlgy connect causing a direct short in my wiring harness...always frying the wire to the coil. It may be worth a quick look under there.

There is also the issue of your relay board...at one time you said you couldn't get the regulator out...do you have some sort of short going on in that board? Perhaps you could find someone who has a known good spare board that you could try.

Electrical issues suck....

Who ever heard of fusing the output wire of the alternator? If it has been installed right, you wouldn't ever need one. Not the fault of the installing person that the stud's too long, but that should have been caught when the cover was installed. It won't seat properly with that long stud, and that should have been the first clue. The Cap'n

computers for kids: i agree, i wonder if something else fried when i flipped the poles. still, you would think it would have caused the short or whatever it was pretty quickley.. none of the other wires have any burn whatsoever. i did a pretty thorough look-around in the engine bay (what wires are left given that it's carb'd now)

Cap'n: when you say "cover" do you mean the thin piece between it and the fan shroud (the plastic ring) or do you mean the cover that protects the connection point for the wiring as well as the connection for the cooling boot.
i took pictures of everything as i did it and referred to those pictures when i put back in the new alternator to make sure everything was matching up. everything matched up perfectly it terms of fit. i didn't notice any issues with a bolt or rod sticking out.
nobody has mentioned the possibility of the wire housing burning from touching the runner to the carb (1st pic you can see the rubber mark)...is this not a possiblity?
thanks for the help!

It is interesting that the over-long stud has been an issue for so many years.

http://www.914world.com/bbs2/index.php?showtopic=5913

...right! I forgot that the electricity is flowing "backwards" in this situation... D'oh!

Had a wire do that on a car I had (not a porsche) about 15 years ago.........result of a direct short to ground. filled the cabin with lots of white smoke.

I would look at the grommet in the area I circled in green. The wire I had this happen to passed thru an old grommet and finally the sheet metal cut thru the insulation. It is the only thing I know of that will fry the insulation off the entire wire or cable that fast.

Hope this helps,

JimClick to view attachment

just to let you guys know i spoke with jeff who is the guru with wiring harnesses (recommended to me by someone on this board). he confirmed that there must have been a bare part of wire exposed to the engine tin and boom.
i'm going to make this conjecture though.
wire housing touched the runner, melted, exposed the copper wire grounding it to the frame and BOOM there went my alt
i guess i might take this chance to outline installing the alternator without dropping the engine as a DIY with pics and what not.
any interest?

I wouldn't think the intake tube would be hot enough to melt the wire.

My guess is your issue was caused by wire chaffing and the insulation wore through in a location where the cable passes through sheet metal.

Over time, insulation subjected to vibration will be easily cut by the thinness of sheet metal.

I am also guessing that the wire burned through and is no longer connected between the starter (battery voltage) and the alternator. Otherwise, it would still more than likely short where it did when the wire burned. The picture looks as if you didn't tape the bare wire between the engine tin and the starter, or below the engine tin.

You will undoubtedly be able to see evidence where the short occurred due to an unmistakable burn mark that will resemble a bad weld mark.

I have changed an alternator with the engine in the car and it is a PITA. The time consuming portion is removing and replacing all the heater ducting. The hard part is loosening and removing the bolt that acts as the pivot for the alternator.

Good luck with it and I hope it's not too hot where you live. I hate working under the car while sweat pours into my eyes.

from the looks of your photos, the wire had a short to ground either near the point where it goes down through the sheet metal to the alternator (maybe at the retaining tab), or at the alternator itself. The key to finding out where is to see where the burning stopped. Look to see where the burning stopped on each end. One of these will be the culprit. JoeO

updated with pics of why this happened

hard lesson. this came up so long ago i doubt some folks are aware it. it resurfaces every year or so. to bad there isn't some kind of warning list. not like the classic section.

k

There is supposed to be a rubber boot that covers the stud in the alt. if that is not there it will arc across the the metal backing plate.

Not sure if you removed it for the pics. or not

Keith

That boot goes on the stud with the red wire. It is the other stud that shorts out with these rebuilds.

I think it is up to Bosch to fix the problem they have created. These are not a bolt-in replacement for the original alternator.

It's the rear cover (cooling shroud) that shorts on the long stud. Even the "aftermarket" rebuilders put a long stud in and if you're not paying attention .... POOF and the smoke gets let out.