Mikeg72

Well, 1st. outing for the year was like heaven (as usual) loving life.
After about 1/2 hour of driving, close to home the car violently bucked and suddenly quit. Pulled it off the side of the road and I noticed smoke pouring out of the battery compartment. I grabbed my fire extinguisher and opened the battery compartment lid to find the negative battery wire glowing red hot and the insulation on fire! Put it out
quickly with a shot of extinguisher and cut the battery cable.

Phew! Awful glad I always carry a fire extinguisher in the car! No damage at all after I hosed off the battery & battery compartment other than a fried battery cable.

Any ideas where to look? Also, would it be a good idea to add a fuse or fusible link
Inline (just in case)? What amperage fuse would I use?

Thanks!

Mike

SIXFOOTER

your going to need to have that battery tested and get the alternator tested also. Replace the cable and nake sure to get or make one that is the same size or even better 1 size larger.
The battery either tiik s sheite and was drawing to much current thru a bad battery connection, or the alternator went wild and was putting out to much current and that found the same bad battery connection. There is only 1 reason for the cable to light up like that and its to much current. That can be either because the alternator is producing to much, or a bad connection on the cable.
What year is your car? The way mine is wired there is a fuse link from the alternator to the battery, its an 81. That would have burned open no problem if the root cause had been the alternator, or the battery.
If the battery shorts internally, it could to the same thing, it will draw a Huge amount of current off the alternator.

mrvette

THE ONLY thing that will fry a cable like that is a direct short from positive cable to ground.....the two ends of that cable are one on the battery of course, the other on the starter solenoid with a much thinner fuse link or maybe even a FUSE leading to the main harness....

you issue is that somehow that + wire is shorted to ground...either pinched in the tranny tunnel, or the starter is fried but good....either way, if the + wire is thicker than the negative wire going to ground at the chassis under the batt box....the thinner wire will fry.... the engine is grounded to the chassis by a ~6" piece of battery cable under the pass side engine mount.....

I think there is no way any alternator condition will fry any battery cable without first frying all the thinner harness wires under the hood...

I think the old battery cable maybe resting on a header?? something loose letting it droop that far, and it welded itself but good....damn wires tend to do that....arc and stick while the damn world goes to hell around it....

Bullshark

Danny, I'm not following your logic?? If the battery developed an internal short, and tried to pull large current from the alt., wouldn't the smaller gauge wire from the alt to the starter go up in smoke first?....not to mention the fusible links. That would also be true if the alt developed a short. Assuming the engine wire harness is ok ( aka the one with the alt charging wire), I am betting the large positive battery cable that connects down around the starter developed a short to ground. Either via the starter or shorted cable. What am I missing?

Bullshark

P.S.
Ok, Gene, sounds like you are on the same thought track

SIXFOOTER

Your correct unless the battery cable that fried had a bad/marginal end on it. In that case the battery drawing its normal current may have been more than the marginal cable end could handle on a continous basis, it heated up and eventullt fried. The alternator wire might still be fine.
Didn't he say it was the Neg cable that burned?
I don't see anything in my battery box for the + cable to short to in order to get that kind of burn, maybe somewhere on the frame under the box? Starter also a good place to look for that. If it was the + cable that shorted and caused the Neg cable to burn it wouldn't necessarily affect the fuse links.

Bullshark

Your correct, He did say neg cable. I didn't pick up on that. That does most likely point to a high resistance connection in the neg. cable. I have seen this happen with those aftermarket clamp on battery terminals when they corrode and loose their low resistance connection. The high connection resistance gets red hot and starts burning the insulation. I do find it hard to believe that the normally small load that the ignition/ day time accessories, would pull while running, would be enough current to make that large gage wire glow read hot. Smoke and hot at the connection, yes.....but glowing red hot wire????...that stinks of a short somewhere. That kind of load would surely fry the positive wire harness feed wires I would think. I am not that familiar with lead acid battery failure modes but I guess if the positive side of one of the cells shorted to ground, it could pull a lot of current through the neg. cable. He might be lucky the battery didn't blow first. Seems low probability though Again, it could also be a short in the positive cable somewhere between the starter and positive batt termisal.



Bullshark

7T1vette

If the short was internal to the battery, the cable connected to it would not be "glowing". An alternator can't put out the kind of current necessary to do what occured. IMO, there had to be a dead-short of the positive battery cable to chassis ground or a dead-short in the starter/solenoid for such a problem to happen.

kaiserbud

MotorHead

I agree, a dead short somewhere, positive hot wire to the starter melting on a header or exhaust, just an example, but all battery energy is just going from the positive cable thru wherever the short is to the negative cable burning it up

CorvetteDave01

It may be your fuseable link from the starter power wire have been removed like mine were. Accident waiting to happen.

RunningMan373

Look for a short on the positive batt cable from the batt to the starter.

Mikeg72

I had the alternator checked out and it passed so I would think it's not
a factor. Checking the remaining wiring, I spent hours looking over every inch but I found absolutely nothing out of the ordinary. The dammage was limited to the wire off the battery which goes to a frame bolt. From there, it's fine. One thing, that wire off the battery is 4 AWG and the wire going from the frame bolt at the rear of the car to the front is a 1 AWG. I don't know alot about wire but I understood that you shouldn't mix wire sizes. This happened after driving for 30 minutes but could the wire size have anything to do with it?

Thanks for all your input!!

Mike

RunningMan373

They do get resistive and corroded. The one I pulled off of mine was pretty well shot. Recommend getting two ground cables, the - batt to frame one and the one between the engine and frame. You can order exact replacements but in the mean time, if you want to drive now, you can go down to local parts store and get some appropriate length batt ground cables, in the plastic packages, with a flat with a hole on both ends for the engine to frame and one with a top or side post and a flat with a hole in it, for the - batt cable.

Also do this, get a tube of 3M electrical grease and some med grit sand paper, when you remove the old cables, sand the hook up points till you see silver metal, wipe it off with a clean, dry rag, then put electrical grease on the spot. Then torque down the cables pretty well, using the lock washers. that'll give you a good connection for your main grounds, makes all the difference. I'm betting it was a resistive neg gnd cable due to corrosion.

Also the 4 gauge should be ok for driving, it wasn't the gauge that caused this.

Mikeg72

I will also take the strarter motor out and take a good look at the positive wire. Since it's so tight between the manifold & block, I can't
really get a good look at what's going on visually.

I'll keep ya posted.

Thanks!

Mike

7T1vette

You should also replace the starter solenoid. Disassemble the old one to see if there is evidence of internal shorting. You really need to find the cause of this problem, or you could experience the same thing later. Having too small a wire in there would cause excess current draw...but only for the time the engine took to start. You need to locate a source of constant current draw...a dead-short somewhere. I would be concerned with burning the car up [or worse] if you can't find the source.

Mikeg72

Will do..

Mikeg72

I installed new battery cables and ran a continuity check and it showed a dead short. I traced the positive battery cable to the starter motor and removed the motor. I found The heat shield had worn a hole through the positive cable insulation and it shorted there. I'm very fortunate to have had the fire extinguisher on board when it happened. I would have been standing on the side of the road watching my car burn up. That $15.00 fire extinguisher saved my baby...

Can't thank you guys & gals enough for all your help, it ultimately sent me in the right direction to resolving this mystery.

Thanks again!

Mike

MotorHead

Another one for the fridge

kdf1986

Good job on finding out the source of the problem, and thanks for posting what this turned out to be. I may be adding new battery cables to my list of things to do this summer.

kdf

kaiserbud

Good thread - makes you realize how the overlooked fire extinguisher is REALLY WORTHWHILE.