soldering copper wire that has black oxide coating

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ever strip away insulation on stranded copper wire 10 gauge or smaller and see that the copper is black?
I have this on the trailer wiring on my truck, I just put a new 7 pin connector back there and cut the oem plug out and stripped all the wire ends. All the wires were fine except for the 10 gauge ground wire which has white insulation.
i googled "soldering black copper wire" to see what some of the reasons causing this are and solutions.
In my case it's not because the wire has black insulation, it is white. It does seem to have something to do with being a ground wire. Other reasons i've read are battery acid or chemicals wicking up the wire, I doubt this is it given the location of the wires. so does anybody know what causes this and how to get rid of it so you can flow 60/40 solder on the wire?
 
I'm not familiar with black coatings on copper. But when in doubt, you must remove all coatings from copper wire before soldering. Is this coating present along the entire length of the wire?

The only thing I'm familiar with that can blacken copper is sulfur compounds.
 
Sorry, for I'm not aware/never heard of black copper wire and soldering.

The closest I can think of (based on my restoration of vintage tube radios in the past) would be severely oxidised copper, which, you'll have to get an Xacto knife's back to scrape off the oxides to expose the fresh, copper-coloured copper before soldering.

the other posssibility would be low quality PVC coated copper wires, where the plastic may have melted onto the copper surface itself, causing all sorts of soldering difficulties.

Regardless: scrape off the black coloured coating and see if you can expose some fresh copper?

Q.
 
I've seen it happen too. Clean it off before soldering or making any connections. Scotchbrite pads or steel wool work great.
 
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I've seen plenty of old electronic gear with blackened copper wiring... As mentioned use a Scotch Brite pad or fine sandpaper to clean the oxidation then solder, otherwise you're gonna be replacing it...

BTW almost forgot, I used vinegar & salt to clean pennies when i was a kid, dunno if it will help in this instance though...
 
I'd say you have a corrosion issue if your wire isn't copper color. The best thing to do is to cut the wire back until you find good, solid wire with no corrosion. Corrosion will always lead to high resistance and heat and ultimately circuit failure if not corrected.
 
The copper wire has been exposed to sulfur, either sulfuric acid or a sulfide from an airborne source.

Remove the black with sandpaper or a wire brush, coat the clean copper with vaseline or with a chemical that renders it inert (tin coating from solder, for instance) and then make your connection.
 
The wire blackened because the insulation wasn't able to shield the copper from the outside environment properly.

With solid wire, the corrosion can be easily scraped off prior to soldering. With stranded wire, it is more diffilcult, so I don't even bother. I use crimp connectors when I encounter corroded stranded copper wire and the pressure from crimping bites thru the corrosion and into fresh copper.
 
Acid flux like you get with silver solder works well also. But if it is 10g solid wire sand paper or a scotch brite will work well. Other things that work are kitchen cleaners like Brasso or Bar Keepers Friend.
 
I also ran into this over the weekend when I replaced a few terminals and freshened up the grounds on my old Landy. It was only on a few wires, some in the wheel wells and inside the cabin...no rhyme or reason that I could see.

I was going to Scotch Brite the wire, but it would only reach the outer strands' outer surfaces and I was concerned that the solder may not adhere or wick up to the inner strands which were not cleaned. I considered various cleaning solutions but I was also concerned about leaving some residue and potentially causing another problem down the road.

I elected not to solder but used a good quality shrink tube crimp connector packed w/ dielectric paste. I've had good luck w/ this in the past.

w
 
i can't cut the wire back, it's in the factory loom and i don't even want to call the dealer to see how much that wiring back to the connector would cost.

not sure if i explained in detail enough the first time, but this is just the 10 gauge ground wire, stranded, with white insulation at the back bumper that is part of the factory trailer wiring harness. I removed the oem 7-pin bumper plug and put a new one on there with yellow/brass connectors. The oem one was aluminum/tin colored and corroded. There are 6 other wires there and they were all fine. The 10 gauge blue and red wires were fine, and the smaller ~16 gauge wires were fine. So it seems it has something to do with the grounded side of the electrical system more than anything else, and what sketchy info i got on the web all leaned toward ground wires having this problem than hot wires.
I can't see how sulfur or other airborne contaminants could have caused it and not affected any of the other wires given the location. And because it's stranded, I can't easily sand or scotch-brite it. I've tried and it does not scrape off easily if at all. i did take one strand from a cut piece about an inch long and soak it in an ounce of white vinegar for about 30 minutes and the black went away and it was clean. will see if solder flows onto it later with and without flux.

but i've run into this issue many times before with wiring either on cars or boats and in a lot of cases i've cut the wire back many inches to many feet and the stranded wire is all black. You can crimp a connector onto it and it's fine electrically but solder will never go onto it no matter how hot you heat it even if you use flux.
 
found this, again seems something to do with ground wires
http://www.nachi.org/forum/f19/black-copper-wire-45334/

these were exposed ground wires. in my case, my ground wire was insulated. find it hard to believe sulfur caused this, if it did why doesn't it affect nearby wiring also?

and other spot on the truck was the wire to the solenoid on my starter. That was purple insulation i think, 14 or 16 gauge. Had to redo that connector because it was all rusted so i cut that wire back about a foot to solder new wire onto it and it was blackened all the way back. just used a butt crimp, new piece of wire with ring terminal to solenoid and that has worked fine for last few months. so in this case it was not a ground wire.
 
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Also, materials/chemicals can creep inside insulated stranded wire.
Plain old Silicone RTV has acetic acid [vinegar], and is specifically prohibited from copper wiring, as it can damage and migrate.
 
i will stick some rtv on a clean piece of wire tonight and see what happens.
 
Different gauge than the rest so it's probably from a different supplier than the other wires; it would make sense to "cheap out" on the largest gauge to save money. Either the sulphur came from your exhaust and permeated the insulation of the wire (an insulation problem), or was part of the insulation (outgassing) and the wire never had a chance no matter what environment it was used in.
 
Originally Posted By: 1 FMF
i can't cut the wire back, it's in the factory loom and i don't even want to call the dealer to see how much that wiring back to the connector would cost.

not sure if i explained in detail enough the first time, but this is just the 10 gauge ground wire, stranded, with white insulation at the back bumper that is part of the factory trailer wiring harness. I removed the oem 7-pin bumper plug and put a new one on there with yellow/brass connectors. The oem one was aluminum/tin colored and corroded. There are 6 other wires there and they were all fine. The 10 gauge blue and red wires were fine, and the smaller ~16 gauge wires were fine. So it seems it has something to do with the grounded side of the electrical system more than anything else, and what sketchy info i got on the web all leaned toward ground wires having this problem than hot wires.
I can't see how sulfur or other airborne contaminants could have caused it and not affected any of the other wires given the location. And because it's stranded, I can't easily sand or scotch-brite it. I've tried and it does not scrape off easily if at all. i did take one strand from a cut piece about an inch long and soak it in an ounce of white vinegar for about 30 minutes and the black went away and it was clean. will see if solder flows onto it later with and without flux.

but i've run into this issue many times before with wiring either on cars or boats and in a lot of cases i've cut the wire back many inches to many feet and the stranded wire is all black. You can crimp a connector onto it and it's fine electrically but solder will never go onto it no matter how hot you heat it even if you use flux.


Yup! sounds like airborne related corrosion (polluted air). This is esp. true if the wiring comes close to the ground level (ground ozone), or close to the tailpipe (where exhaust laden with acid and moisture comes to attack).

This was a rather prevailent issue back in the high sulphur days (high sulphur content in gasoline, or diesel fuel) where copper wiring, be it tinned or not, close to the tailpipe or so, becomes oxidised or corroded in due time.

With low sulphur fuels in NA these days (both gasoline and diesel), it's less of an issue (still an issue though).

The only way to overcome this is to solder the connectors (where copper wires meet the connectors) and then seal them off, 1 by 1, with either liquid vinyl tape or RTV silicone (non-acid solvent based type).

For actual connection part of the metal (for trailer connectors, etc.) I typically coat them with liberal amounts of silicone dielectric grease).

Q.
 
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