I am getting fed up. I have been posting a lot of different electrical issues lately. I am super confused. Here is a the summary of what has happened.

I have been running my car without an alternator since I rebuilt the engine. A few months ago, I installed a known working alternator (it didn't come with the little black resistor that is inside of the alternator so I took one of another (non-working alternator). Car started and ran fine. Voltage was around 13.2. Was driving around the neighborhood, had a huge amount of smoke from the engine bay. The wire from the alternator to the starter was torched.

Thinking the alternator was actually not good, I got a new alternator (my friend got it for me for free). It too didn't have the little black box so I took the one out of the other alternator and installed it in the new one. I tried to purchase a new one however they are no longer available. I also purchased a new alternator. I installed the new alternator and my fuel pump started to only work intermittently. Thinking that my fuel pump was simply bad, I just hooked up a different pump that I had. Once I got the "broken" fuel pump out, I hooked it up to 12v volts and it ran for a few seconds then died. Tonight, I tried the same thing except running gas through it and it ran however the pressure was low.

Since I thought that my problem was actually the fuel pump, I went ahead and reinstalled the new alternator. I was driving around the neighborhood for a couple of minutes. Ran fine. Parked it in the garage. When back and touched the alternator to starter wire to see if it was hot- it was not overly hot. I decided to make some timing adjustments. When I turned around to get my timing light, the wire from the alt to starter caught fire!!! I had a fire extinguisher right there. I put it out an inspected everything. It looked exactly like what happened witht he original alternator.

I have no freaking idea what is going on here. Any ideas?

Not sure what is going on, but the wire melting from the starter to alternator melting I would think is current flowing from the battery to the alternator.

Only the battery has the capacity to produce that much current to melt the wire.

There isn't much between the wire and the alternator except the alternator.

The alternator would not be able to produce that much current. The diodes in the alternator would fry before the wire does.

So this points to some type of short circuit from the wire to ground. Check the cover on the back of the alternator.

I caused a fire in my 914 too

wire direct from battery grounded by accident due to lack of rubber grommets, wear and tear, insulation breach etc.
All those amps into one wire w/o any fuse or relay = melted, fire
BTW, i read this board all the time before buying my 914 and already had a fire extinguisher in the car, ready for to halt any potential "car-B-Q"

I agree with above statements: it is likely your battery that over-juiced something

Porsche engineers were smart. Rebuild what they created, and you'll be fine. Skip stuff, and well, you know...

Good luck

I checked the cover and I did not see any major issue. This sounds far fetched but is it possible that the wire from the alternator to the starter could arch from wire to the tin- eventhough the wire insulation is intact? Since it was just installed temporarily, I did not install the grommet between the wire and tin. That is where the wire was most damaged (the copper was actually melted at that point) on the first and second alternator. I am certain that the insulation was intact.

Did not see this before my last post. SO could simply not having the grommet be an issue?

Are you saying you saw melt damage at the tin? Was the wire damaged from the tin to the alternator? I think you found the issue.

BTW, 12V is not enough voltage to cause an arc across an air gap. However, if the insulator on the wire is damaged, touching the wire to the tin will cause immediate overheating and wire and insulation melting. Basically, you're welding with media that isn't designed for welding.

Here are some pictures of the problem areas. I do not recall if the tow melted copper areas were positioned at the tin or the yellow wire fromt eh relay board to starter. I had this issue with my first alternator.

All of the white/yellow dust is from the fire extinguisher.

I do not see any burnt area on the tin. The stater end and alternator end of the wire was the least charred.

Is it possible that if the Alternator to starter wire were to touch the yellow wire to the start- could that cause this issue- eventhough the insulation on both wires was intact?

I am certain that the starter wire to alt wire insulation was intact- it was a brand new wire with almost no miles on it.

It's obvious that this is a short of some kind. Could be that some other wire inside the alternator jacket is melting it's jacket first and then touches the wire you've seen on fire. I'm just speculating here.
this is too complex and dangerous to solve over the forum.I strongly suggest you have a potent electrician look at your problem before you burn the car.

I agree about te safety issue. Unfortunately we only have impotent electricians around here-lol. To address the safety issue, I simply removed the alternator. I really don't need one. I don't drive far so I just charge te battery each night. I would still like to figure this issue out just for curiosity's sake- even though I'm not planning on using the alternator anymore.

The battery wire at the alternator fed the short. Follow the burnt wire to wherever it started to melt. Looks like a direct short to ground. Pinched or chafed wire to the chassis.

Just another reason I run a master fuse and disconnect switch on my car.

Looks like a direct short to ground to me too...

BTW, the alternator charge wire on a 914 normally does not go directly to the starter. It goes directly to the battery.

Electrically this is the same circuit but the wire has to travel through the tin to get to the starter. Perhaps this is where you short occurred?

Another possibility is you caused the short at the alternator. Too many times in/out, since the wire connected to the starter, that connected to the battery... Direct short. =Burnt wire

I agree, that is a direct short and I'm sure your generator diodes are toast. This happened to me, when my fuse box broke and shorted to chassis ground. I don't recall a wire going from the altenator to the starter. Keep looking for other melted wires, and you should ohm out the relay board

Looking back at the ring terminal... Looks like shrink tubing. Not factory Porsche. When you fix it, run the alt wire to the positive battery terminal.

You don't need to charge the starter anyway...

Last I checked the big red cable in the alternator harness runs from the alternator to a lug bolt on the starter solenoid shared with the battery+ cable. Stock factory set-up.

tornik550,
Looks like your alternator wire shorted to ground! It would not have burned like that if it shorted to the yellow wire. When I had my engine out, I replaced that alternator wire because it was hard and brittle. I expect yours was the same prior to the fire. Insulation loses it ability to insulate over time and your changing the alternator probably just finally got the wire to break down enough to short and cause the fire. The issues you were having prior to the fire really indicate a problem slowly getting worse. It was the wire, not your alternator that caused this.
There is no reason for you to run no alternator. Install a tested good alternator and replace the large red wire with an 8 or 6 gage wire and be sure to use that grommet in the tin.
Tom

long ago, early in the old club days there were a number of replacement alt problems that involved (iirc) the stud with the black wire and nut making contact with the rear alt cover. the solution was to dimple the cover outwards at what would be the the stud contact point. perhaps the smoke has obscured the arc point and once the BIG melt off started the current found a path other than the stud. your car didn't burn to the ground taking your house with it, so that is a blessing. are the alt harnesses common for all years of 4 cyl production?

k

Alt harnesses are all the same AFAIK.

If a harness is needed, send me a PM. I'm sure I may have a couple laying around.

me too. still connected to alts.

k

Take Slits up on his offer of a harness; I've got a few alt's laying around , pm me if interested. Tom, Mike and Jeff are top notch electrical references for our 914's. When you hook up your next alt and harness you need to check for draw down immediately with your test meter, not by touch. Keep posting.

You need to add the in line fuse box at the battery one of our members sells. I plugged the yellow starter wire to the wrong side of the starter and the blown fuse alerted me to the problem without a wire fire.

Everyone should have this.

Good luck.

The first harness that I used was a factory harness however it was old and brittle. So that could have caused an arc. The recent episode that I had was from a new wire that I made. I used a 10 gauge wire. I am certain that there were no breaks in the wire cause it was brand new. Is it possible that the wire gauge or insulation was not sufficient causing this issue?

I did not see where the wire arc'd. My goal was to get the fire out. On autopsy- it appeared that both arcing incidents occurred around where the wire goes through the tin however I do not see any marks on the actual tin.

Who sells the inline battery fuse? I think I need one asap!

10 gage (AWG) is too small for the current that cable requires. The factory wire was 6.0mm^2 (metric), so an 8 gage is the correct AWG size, it would be slightly larger than the metric size. Using the 10 gage was at least a problem, if it didnt cause this fire.

The most common problem I see with these 40 year old orignal alternator harnesses is brittle/cracked casing and broken wire insulation exposing the conductor(s) at the point where the harness passes through the tin...where its hard to visually inspect and where its most vulnerable to a direct short to ground or to the other wires in the harness. Please carefully inspect your alternator harnesses at this critical location, even if your grommet is in good shape.

It looks very much like the insulation failed at the point where the wire entered the alternator, shorting to the case, which is grounded. Inside the case, the insulation is fine because no current went through there. If there was a rubber grommet at the alternator, it failed/cracked. If not, vibration quickly sawed through the wire.

Great discussion!
To clarify my original reply, now with correct terms, I experienced a short to ground due to break/worn spot of the plastic insulation of an over-sized wire gauge.

The gauge of the wire must be matched to the expected (engineered!) current and resistance. Having a big fat wire was one of my bad choices, lack of a grommet to prevent wear-though of the wire insulation where it passed through metal (grounded!) was the other.

Carry on

I agree with Jeff, 10 gage would be pushing it a little too close to the limit. I think I went with a 6 ga, but maybe 8 ga. Error on the side of caution!! Also keep in mind what type of wire you are using. This is in a very hot area. I would use GXL rated automotive wire. It is intended for use in auto engine bays and is good up to 257 degrees F. Regular auto primary wire is rated for general purpose hook up and the max temp is 194 degrees F. Outside the engine bay is OK for this type of wire with the exception of around the starter area, very warm and just over the exhaust.
I make the fuse block kits, but this problem would not have been protected by the fuse block I make. You need to get an inline fuse set up for the battery that protects the large starter wire. Think of in the neighboorhood of 150 amps or greater.
The fuse block info is at the bottom in my signature area.
Tom

When I had swapped my alternator out for a 120amp unit, Jeff made me a custom harness with 2 8guage wires, you can never be to careful.

THE THREAD has a lot of pictures comparing the stock wiring from the alternator to the new wiring.


Good luck with your electrical problem.

What other fuses do we need Tom and can you make them for us?

Ignition switch
Main power relay
FI ECU
Starter motor
Alternator
Headlamp switch
Fog lamp indicator bulb
Seat belt warning buzzer
Fasten seatbelt bulb

What did I miss?

Jeff,
The fuse block kit I make basically prefuses everything except the starter motor and alternator. The starter and alternator would require a large fuse at the main wire for the starter and the small indicator bulbs would need small inline fuses to protect the small wires feeding them ( say 3 amp). If the small bulb circuit shorted to ground, the resulting instantanious high current would cause one of the 4 fuses at the fuse block to blow. A medium overload of 15 amps would most probably cause the circuit wiring for the bulbs to overheat and catch fire. The kit I put together puts fuses back at the battery for the 4 red wires from the battery positive. It protects all of the wiring harnesses from a short circuit from there.
I thought you had seen my fuse block thread?
Tom
PS: what is the smiley devil for? Am I missing something?

I inspected my system a little better today during the daylight. I found a few things that I did not see last night. I did not see any charring on the tin. I did however find some charring that I did not see last night. Please see below picture. Any thoughts?

When the fire started- I heard many pops. For some reason, the wire heated up, melting the insulation, then it started arcing to various ground points. The closest was the tin however I do not think that the tin was the primary source of the issue. My 10 gauge wire was a problem however I really think the grounding issue came from somewhere in the alternator. Do the char marks point to anything? I really think my black box has something to do with this.

Wow, looking at that, it looks as if the 10 gage wire lying across the (black box) got hot enough to melt part of the black box. This probably shorted your 12v from the battery to ground or close enough to it to cause a fire.
Tom

Is it possible that my alternator simply is grounding to the tin properly? My fan shroud was painted by the po. Is it possible that if it has poor grounding, the alt to starter wire could overheat and cause the fire?

How can I check to see if my alternator is grounding properly?

just a thought; could a "D+ & DF" shorted together via a VR that is stuck/defective, defective harness or relay board lead to any of this??

D+ & DF shorted would cause the alternator to put out full voltage (16V) and likely damage the battery.

Bad grounding at the alternator would only cause the alternator to not produce any current.

Do you have pics of the inside of the alternator cover where the damage is? Also maybe pics a little less magnification of the back of the alternator.

There isn't much in the alternator to cause such high currents to melt the wire. Just a couple of windings and some diodes.

This looks a lot like grounding to the chassis.

Dang, Steve. You need me to come back out and un-fuch this for you? I agree that 10ga is too small, and you obviously have a short, and that you need to check the diodes in the alternator to verify yours are not toast. The alt and its circuit is a very simple one so assure everything is the way it was supposed to be, then change those wires and test. I can talk to you next week about this if you like. On vacation now

I would like to sum things up to see if putting everything in one plays sparks any ideas. It clearly is something that is grounding out. Summary of events below-

-i have tried two different harnesses and both either completely melted or caught fire. This occurred with two different alternators..

I find it difficult to believe that I had a crack in both wires in the same location. One was an old harness that I had used previously with no problems and the other was brand new. Granted the new one had too small or gauge wire but still seems hard to believe that the exact thing occurred with both harness'

-i have tried two different voltage regulators- both are reported to be in working order.

-my new alternator did have long studs however those were ground down and do not contact the alt cover.

-last night, I tried installing the alternator with a new 6 gauge starter to alternator wire (with all grommets in place). when I went to reconnect the battery - connector- i sparked like crazy. I decided to see what would happen if I installed a ground wire from the alternator case to the chassis. I was then able to hook up the battery -ground wire without sparking. I started the engine and everything ran fine. Drove it around the neighborhood- everything was fine. Came back to my garage and everything looked good (no fires) however the tachometer would surg and the idle would surg (however not at the same rate as the tach surg).

Have you checked the ground strap at the trans?

I had this exact problem on a Plymouth Arrow years ago. I had pulled the head for repairs and upon reassembly I did not install the ground strap. It ran fine for several days and just fried the wires. Repaired a few times and replaced alternaters with same results. Finally was told about the ground strap. Reinstalled it and the problem was solved.
David