wire melted....what gives ?

[66moneypit]

Went out yesterday to drive the convertible...nice day for it. I drive it around town for a while and come back. I go back out 10 minutes later and the car barely turns over. It's like it's struggling to turn over. I look up and see black smoke coming out the right front of the grill. Right where the battery is suppose to be. Look at the battery and there are two ground wires. One VERY thick one for the ground to the block coming off the negative terminal. And a small thinner one coming of the negative going to a screw near the headlight. The insulation on the small thinner one had melted and it was fused to the battery. I pull it off the battery and you can see exposed wire. After that the car started right up with no problem.

Not sure if the gauge of the smaller wire was thick enough. I looked at it further today and it looked a little burnt. Shouldn't be a problem replacing it however I'd like to know what might have caused this.

I can see where it is very easy for that wire to sag and make contact with the battery. Is it possible the battery got hot enough to melt that wire ? If so that's a simple fix. Not sure what the other problem could be unless the wire was just old. It was there from the previous owner.

I will confess I haven't looked at a wiring diagram yet to see what this is connected to.

 

[67bluegt]

It may be a bad ground on the main cable going to the block itself, forcing more current through the smaller body ground cable. I would replace the cable to start.

 

[tos]

I would check to see if you have your engine to firewall ground wire still installed. Your engine needs to be grounded to the body too. Look on the back of your heads and see if this ground is still there. Then check all other connections and be sure the battery wires are in good shape and not corroded within the wire strands. If so replace them or they wont carry the proper current.

 

[66moneypit]

I will check to see if the ground to the block is still secure first. Is there a test that I can to see if the ground cable to the block is bad ? Also....is it possible the insulation just melted on the hot battery and caused it to short ? Like I said...once I removed it from being stuck to the battery it fired right up.

 

[Capt Dan]

It made contact w/ the positive side? Probably could have melted or worn thru. If it melted it would be because that wire was too hot (still a problem).

If it was worn, then replace and reroute.

Had an issue similar on mine, but it was a short in my ignition. Started melting wires from the battery back to the Ignition switch.

To check the ground cable look at the ends for corrosion first, and pull on the ends to make sure the crimps are tight.

just my $.02

 

[67bluegt]

I might check the location of the ground cable to the block. Sometimes the original bolt was worn or broken and a later cable was bolted somewhere close like the aluminum timing cover or somewhere less conductive down there.

 

[tos]

Is there a test that I can to see if the ground cable to the block is bad ? Also....is it possible the insulation just melted on the hot battery and caused it to short ? Like I said...once I removed it from being stuck to the battery it fired right up.

You could do a continuity test on the cable if you knew what the resistance was supposed to be but like I said earlier check for corrosion within the strands under the insulation. When these cables get old they corrode under the insulation and wont carry much current. That wire likely melted because it had to carry alot of current to ground and its too small to do so, got hot and melted. Thats what leads me to think you have a grounding problem. Those big battery cables are to carry heavy current say for starting or running amp on your stereo with a thump box. For some reason that little wire had to assist the grounding of the battery.

 

[66moneypit]

I might check the location of the ground cable to the block. Sometimes the original bolt was worn or broken and a later cable was bolted somewhere close like the aluminum timing cover or somewhere less conductive down there.

The ground cable is connected straight to the block and that cable was replaced. That I know for sure. I will double check the bolts to make sure it's down tight....

 

[66moneypit]

It made contact w/ the positive side? Probably could have melted or worn thru. If it melted it would be because that wire was too hot (still a problem).

If it was worn, then replace and reroute.

Had an issue similar on mine, but it was a short in my ignition. Started melting wires from the battery back to the Ignition switch.

To check the ground cable look at the ends for corrosion first, and pull on the ends to make sure the crimps are tight.

just my $.02

Based on where it was fused to the battery, I'd say it never touched the positive. It was literally stuck right between the two post. When I picked it up, the wires were bare from the melted insulation and a little burnt looking.

 

[67bluegt]

Hows the condition of the starter cable from the solenoid? Any chance it's worn or hitting the body somewhere to cause a short?

 

[66Runt]

Continuity tests do not work on main power cables

To test any main power cable do a voltage drop test.

As an example using the cable from the block to the body:
With an analog gauge use the lowest scale that is slightly higher than battery voltage to start (i.e. 15V DC scale). Use Auto range on a digital mulit meter.
Put the positive meter lead on the cable lug attached to the body, put the negative lead on the cable lug attached to the engine. Disconnect the coil and crank the engine over. You should not see more than 0.2V through the cable (but real world I don't get excited until it gets above 0.4V for non-electronic components).
You may need to drop your scale down to actually see the true reading. But I've seen cables so bad that they drop 9 or 10V which is why you start slightly above battery voltage.

I've preached this test for years to dealership technicians. If you can grasp this concept, you will be able to solve all those pesky little electrical issues (like dim bulbs, horns, flashers, etc).

This is a tremendous trouble shooting tool, so I would be more than happy to explain further if needed.

BTW: when it comes to electrical wires in our classic mustangs..."resistance is futile" (done in my best Darth Vader voice)

Scott

 

[Carnivore]

BTW: when it comes to electrical wires in our classic mustangs..."resistance is futile" (done in my best Darth Vader voice)

lol, wrong universe. Thats Star Trek, noob!


/geek mode off





About the topic.. Now I know why its important to have that little ground from the engine to the firewall. I always wondered how important that really was.

 

[66Runt]

Darth Vader isn't a cyborg!!!!!

Guess I shouldn't quit my day job eh?

 

[Max Power]

I am still trying to figure out how a ground wire shorted to ground?

 

[66moneypit]

I am still trying to figure out how a ground wire shorted to ground?

That's two of us.... I am not an expert at all...but this one has me struggling. I haven't had a chance to perform the test that 66Runt mentioned but I would agree with him it's a good test. I have seen it referenced in several places since I ran into this issue.

If I run a few test and it all checks out then it could have just melted from coming in contact with the hot battery.

 

[66Runt]

Most likely didn't "short out"

In order for it to be a short, it would had to have crossed paths with a positive.
Instead of a short, think of it as a resistance point in the circuit. Like someone partially closing the hose bib on a sprinkler.
Now if you did that with a sprinkler, instead of a nice big spray you'd have a little trickle...but what if, your sprinkler could actually suck the water through the hose, so that it would keep a nice big spray pattern?
The hose would finally collapse under a vacuum, because the hose bib valve is partially closed, right?

Well here is one difference between water and electricity, While your sprinkler can not force the water to come through your hose, your starter can force the cable to supply the amperage it needs to run. But unlike the hose, a battery cable can not colapse, so what happens is the resistance point (loose cable lug, or bolt) gets hot, that creates more resistance, causing more heat, causing the cable to have to carry more amperage, which causes even more heat, like a viscous circle, until you have melt down. And it's all because the starter (or head light, or fan, or what ever else is the "load") is able to force the wire, or cable, to carry more than it is capable of.

More than likely what happened is the bolt got loose at the block, or the cable got loose inside of the lug, or corrosion built up inside the cable. This causes resistance (that is the "resistance point" I mentioned, and is just like partially closing the hose bib valve).

The best test for this condition is Voltage drop. And I highly recommend learning this. You'll be amazed at how simple electrical systems really are. Trust me, I can't set the clock on my microwave, but I can trouble shoot some of the most complex electronics out there. And it all started with this fundamental principle (it's actually called Ohms law)

So it can't be rocket science. Otherwise I'd still be holding my meter saying Huh???

So, if I can help, I'd be glad to. You all have provided me with a heck of a lot of good information.

Scott

 

[Max Power]

Sounds like the only explanation would be what runt said, your other grounds are providing too much resistance and you are overloading this little wire.

 

[66newbie]

Are you referring to the fuseable link wire coming off the battery ? Like my name says, I am a newbie, what is the purpose of that particular wire ?

 

[66Runt]

There wasn't a fuseable link stock on a '66

Can you explain where this wire comes from and goes to? or post a picture. Then we can probably tell you what it's for.

 

[pabear89]

I am still trying to figure out how a ground wire shorted to ground?

Power is like water, It will follow the path of least resistence.
The ground short is caused by and overloading draw against the grounding side.

This case it was the cranking draw on the grounding system,
the only good contact at that time was the short 12-14 guage groundwire for the rad support.
The load was to great for it to handle and it overheated like an electric heating element.


PB