Electrical Problems- Caught my car on fire, New Info- please help!!!! (thanks for input so far) Options

[rhodyguy]

me too. still connected to alts.

k

[76-914]

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. (IMG:style_emoticons/default/beerchug.gif)

[bandjoey]

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.

[tornik550]

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!

[JeffBowlsby]

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.

[worn]

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 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.

[Chris Pincetich]

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 (IMG:style_emoticons/default/beerchug.gif)
(IMG:style_emoticons/default/blowup.gif)
(IMG:style_emoticons/default/biggrin.gif)

[Tom]

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

[jsayre914]

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. (IMG:style_emoticons/default/happy11.gif)

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


Good luck with your electrical problem.
(IMG:style_emoticons/default/beerchug.gif)

[JeffBowlsby]

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?

(IMG:style_emoticons/default/happy11.gif)

[Tom]

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?

[tornik550]

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.

[Tom]

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

[tornik550]

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?

[76-914]

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?? (IMG:style_emoticons/default/popcorn[1].gif)

[Spoke]

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.

[Dr Evil]

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 (IMG:style_emoticons/default/smile.gif)

[tornik550]

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).

[Dr Evil]

Have you checked the ground strap at the trans?

[dwillouby]

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