Melted ground wire

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Johnschummer

Johnschummer

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Feasterville, PA
Little backround. Picked Up a 72 cuda 340/auto no motor no trans. Probably sat for 30 yrs, who knows. Already had 72 340 in my garage so I had to have it and the price was right. So I picked up 73 727 off facebook from an 360 charger and did my first auto rebuild. As I rebuild the 340 I thought I should make sure my trans works and all my wiring is in order so I don’t wiping out the cam in my new motor trying to get it to fire. Borrowed an old clapped out 318 that we pulled from my brother duster that we know to run. Slapped it to my fresh rebuilt 727 and patched up the existing wiring harness in the car. Got it fired up and running, shiftin, moving, all is well. So in the mean time I got all the lights working and been fiddling with the gauges, cleaning connections and what have you. The ammeter seems to hang on the high side of center. Checking battery with voltmeter on the 200 setting It was reading like 18.5v but when I put it on 20 setting it was 13.5. So yesterday I decided to throw in a new engine harness I purchased for car and a new regulator since it looked questionable and had incorrect screws and like 3 lock washer per screw and it was pretty rusted. Cleaned up firewall with dremil and used nuts and bolts since holes were stripped. Also note the alternator was from my 69 barracuda that was converted to dual field, mopar unit that had went bad. Took it to a reputable local auto electronic guy who just rebuilds starter and alternator who seemed excited to see an old mopar unit.

To get to the point, ammeter didn’t change really and voltmeter still showed super high in 200 setting but at the 20 setting it was about 13.5. Figured Im not understanding what the difference in each setting is although I thought it just added decimal places to your reading and that all is good. I started it today to take ride around block, so I threw on negative cable and hit the key. Starter sound funny like it locked and then went which it s never done. Thought cable was loose so I gave it a twist, cranked it fire up no problem. Let it warm up about 5 min and jumped in, put it in gear went to pull out and car completely shut off. Figured negative cable was loose, went to check it and the 10 ga that goes to firewall was melting and smoking. Pulled cabled and started inspecting other wires. No visible damage. gave it minute to cool, pulled melted 10ga from main ground and tried touching it to neg terminal and it was sparking bad. Unhook everything and pushed it up driveway Went in for dinner. Came back out after dinner touch negative cable to terminal and no sparks. Car starts right up. Put voltmeter on battery 24.5 v on 200 setting 13.5 on 20 setting. At this point I’m totally confused, so I check battery on my 69 barracuda stock wiring although upgrade to dual field with voltmeter in both 200 and 20 setting and 13.5 and 13.50.

so what’s up with my meter reading?
could the high voltage be what melted the ground?
could it be the starter? although a brand new 400$ mcrobb unit I bought for my 65 barracuda for my TTI header that I keep procrastinating to install. Not to say that means it ain’t junk.
could it be the fact that I don’t have battery cables super tight? Also note I do not have a firewall ground to head, didn’t see provisions at firewall and I didn’t see one in factory diagram, and figured thats why they added one from battery to rad support, not saying that’s right but I assumed it.

couple photos below. Note I’m using the black 200/20/2 on the right of the voltmeter. I believe that’s correct but I am a dumb carpenter.

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How many other ground wires are there?
 
I thought that initially but there is a 200 in red also which I figured was a/c Also doesn’t explain why my 69 barracuda read 13.5 or 13.50 in both 200 and 20 in black
 
Just the one from battery to rad support. I assumed since my 69 has no ground at battery to rad but does have one engine to firewall that Chrysler moved it sometime in 1970, also mancini carries firewall grounds only to 69, nothing later. But again I was assuming
 
"The 200 is for A/C power and 20 is for D/C power that’s why it jumps like that"

There are 2 - 200 v ranges one red and one black. the black 200 range should read the same as the black 20 range. The thing about ranges is measuring a small voltage on a higher voltage range results in a less accurate reading

Example...

(Just made up numbers for example only)

1.5v on the 2v range would read 1.523

1.5 on the 20v range might read 1.5v

1.5v on the 200 v range might read 2v
 
As for why did your ground wire melt...

It became a fuse.

It did not have sufficient current carrying capacity for the load being pulled.

10 gauge is not all that big, typically the ground straps are branded copper straps.

It would not hurt to add additional ground to body straps.

Without them you could be using your transmission and linkage or another path to ground.
 
Dana67Dart said:
"The 200 is for A/C power and 20 is for D/C power that’s why it jumps like that"

There are 2 - 200 v ranges one red and one black. the black 200 range should read the same as the black 20 range. The thing about ranges is measuring a small voltage on a higher voltage range results in a less accurate reading

Example...

(Just made up numbers for example only)

1.5v on the 2v range would read 1.523

1.5 on the 20v range might read 1.5v

1.5v on the 200 v range might read 2v
Click to expand...
Yeah, that’s what I meant. The red Vs black and then the volt scale. the 200 should be used for higher DC volts like 48v, where the 20 should be used for 12 volts and such.
 
Johnschummer said:
Just the one from battery to rad support. I assumed since my 69 has no ground at battery to rad but does have one engine to firewall that Chrysler moved it sometime in 1970, also mancini carries firewall grounds only to 69, nothing later. But again I was assuming
Click to expand...
That's the only one besides the negative battery cable? Yeah, that's not enough.
 
Dana67Dart said:
As for why did your ground wire melt...

It became a fuse.

It did not have sufficient current carrying capacity for the load being pulled.

10 gauge is not all that big, typically the ground straps are branded copper straps.

It would not hurt to add additional ground to body straps.

Without them you could be using your transmission and linkage or another path to ground.
Click to expand...
Understood, i will add one at firewall but based on voltmeter clarification. I definitely am seeing like 24.5 v in 200 dc (flat line w/ dashed line under it in black) and 13.5v in 20 on this 72 cuda and my 69 barracuda is 13.5/13.50 in both settings. Something is off there that I can’t wrap my head around
 
1704251113574.png

Johnschummer said:
Figured negative cable was loose, went to check it and the 10 ga that goes to firewall was melting and smoking.
Click to expand...
Something is seriously wrong.
A short 10 gage wire should handle 55 amps without melting.

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Johnschummer said:
pulled melted 10ga from main ground and tried touching it to neg terminal and it was sparking bad.
Click to expand...
That means that there is a short.
Key off, all switches off, connecting the ground wire to the battery should not spark. Somewhere a circuit was complete.
With over 55 amps going through that wire, my guess is a battery hot wire was grounding.
If you looked at the ammeter, was it showing maximum disharge ? If not, the short is before the ammeter. (in other words between the battery positive and the ammeter)
Johnschummer said:
Came back out after dinner touch negative cable to terminal and no sparks.
Click to expand...
Something happened during cooling off or when you pushed it so that the short was no longer touching.

I would NOT add bigger wires. I don't see fusible links, so would add them where they ought to be.
For hunting the problem, you may want to use a lamp and/or a circuit breaker.

Any of the wires shown here are hot with the battery connected.
Any of them touch ground and with the negative connected to the battery, the circuit is completed.
1704252344457.png


So these are the wires I would begin looking exposed conductors, hanging loose, and obvious signs of contact with the body.
Pinching is another favorite way for Murphy's Law to find a way to short circuits.
Further, since the body ground is the one that got hot, the short is unlikely to be the alternator or on the engine. Grounding to the engine should have resulted in the high current flowing through the big ground cable.
 
Last edited:
Mattax said:
View attachment 1716187040

Something is seriously wrong.
A short 10 gage wire should handle 55 amps without melting.

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WireSizer User Guide for iOS (iPhone), macOS, iPadOS & Android.
www.wiresizer.com www.wiresizer.com


That means that there is a short.
Key off, all switches off, connecting the ground wire to the battery should not spark. Somewhere a circuit was complete.
With over 55 amps going through that wire, my guess is a battery hot wire was grounding.
If you looked at the ammeter, was it showing maximum disharge ? If not, the short is before the ammeter. (in other words between the battery positive and the ammeter)

Something happened during cooling off or when you pushed it so that the short was no longer touching.

I would NOT add bigger wires. I don't see fusible links, so would add them where they ought to be.
For hunting the problem, you may want to use a lamp and/or a circuit breaker.

Any of the wires shown here are hot with the battery connected.
Any of them touch ground and with the negative connected to the battery, the circuit is completed.
View attachment 1716187046

So these are the wires I would begin looking exposed conductors, hanging loose, and obvious signs of contact with the body.
Pinching is another favorite way for Murphy's Law to find a way to short circuits.
Further, since the body ground is the one that got hot, the short is unlikely to be the alternator or on the engine. Grounding to the engine should have resulted in the high current flowing through the big ground cable.
Click to expand...
It SHOULD unless the ONLY other ground wire is somehow not making a good connection.
 
I think the meter is not accurate. Maybe the range switch is iffy. It should be more accurate on the lower V scale

It might be possible the ground (larger) cable from the battery to the block is actually bad. They can corrode internally and you won't see it. Also possible that paint, etc, prevented a good block connection.
 
RustyRatRod said:
It SHOULD unless the ONLY other ground wire is somehow not making a good connection.
Click to expand...
Doesn't matter in this case.
Short was occuring with key off.

If the starter was running, and the engine ground cable was poor, then yes, the body grounds would try to carry the current.
In that case I'd agree the problem was a poor engine ground.

But in this case its big current with the engine running, and then even with the engine off.
That 10 gage ground is capable of handling pretty much every device running at the same time. Lights, heater, wipers, radio, horn, brake lights all at the same time is roughly 30 amps. All those electrons will flow back to the battery at the same time though the same wire. Or if the engine is running, then onto the engine ground to return to the alternator. Either way a 10 gage wire should easily handle that.

Sure there also should be a engine to firewall ground, so two paths, but that's not the heart of the problem here.
 
Mattax said:
Doesn't matter in this case.
Short was occuring with key off.

If the starter was running, and the engine ground cable was poor, then yes, the body grounds would try to carry the current.
In that case I'd agree the problem was a poor engine ground.

But in this case its big current with the engine running, and then even with the engine off.
That 10 gage ground is capable of handling pretty much every device running at the same time. Lights, heater, wipers, radio, horn, brake lights all at the same time is roughly 30 amps. All those electrons will flow back to the battery at the same time though the same wire. Or if the engine is running, then onto the engine ground to return to the alternator. Either way a 10 gage wire should easily handle that.

Sure there also should be a engine to firewall ground, so two paths, but that's not the heart of the problem here.
Click to expand...
It was kinda hard to follow. I missed it was occurring engine off.
 
A
Mattax said:
View attachment 1716187040

Something is seriously wrong.
A short 10 gage wire should handle 55 amps without melting.
[/URL]


That means that there is a short.
Key off, all switches off, connecting the ground wire to the battery should not spark. Somewhere a circuit was complete.
With over 55 amps going through that wire, my guess is a battery hot wire was grounding.
If you looked at the ammeter, was it showing maximum disharge ? If not, the short is before the ammeter. (in other words between the battery positive and the ammeter)

Something happened during cooling off or when you pushed it so that the short was no longer touching.

I would NOT add bigger wires. I don't see fusible links, so would add them where they ought to be.
For hunting the problem, you may want to use a lamp and/or a circuit breaker.

Any of the wires shown here are hot with the battery connected.
Any of them touch ground and with the negative connected to the battery, the circuit is completed.
View attachment 1716187046

So these are the wires I would begin looking exposed conductors, hanging loose, and obvious signs of contact with the body.
Pinching is another favorite way for Murphy's Law to find a way to short circuits.
Further, since the body ground is the one that got hot, the short is unlikely to be the alternator or on the engine. Grounding to the engine should have resulted in the high current flowing through the big ground cable.
Click to expand...
You got me wondering if the starter wire got melted to exhaust. In the dark last night I didn’t take notice. I’ll check when I get home from work.
 
Plus, that car looks to have some serious rust issues. So, is all of the electrical in the same shape?
 
CRUZE 418 said:
Plus, that car looks to have some serious rust issues. So, is all of the electrical in the same shape?
Click to expand...
pos/neg cable new, engine harness new, next will be front lights, then dash, rear light. Honestly aside from the engine harness that was butchered dash harness is the best I’ve seen of the 5 old mopars ive owned. i always replace all the wiring on these car just to keep my sanity, just a big nut to drop all at once.
 
I have update. Looks like my starter wire was shorting out on my center link. One of two thing happened and I’ll have to further investigate when it’s little warmer.
center link was always rubbing wire, finally wore hole thru casing and shorted it out
or that fancy McRobb starter which is clockable rotated it self (clunk I heard when starting before ground melting problem) because I never torqued it properly to hit center link. Finally put 2 and 2 together when started after work today and ran fine for 10 min, then I went to straiten wheels and I stalled out. Same thing last night when I pulled out I have to steer around another car and it conked out and wire began to melt.

thanks everyone for the help,looks like I have some cable replacing?/rerouting to do. Still not sure what’s going on with my multimeter. on the battery with car running my 2 other barracuda read same number in 200 and in 20 setting but this 72 reads normal in 20 but it’s all over the place in 200 setting. I snapped some photos, seeing numbers up 60s. Notice the setting on multimeter

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I wouldn't trust that thing. You would expect the resolution to be a little better on the lower scale, but that is excessive.
 
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