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I noticed an insulating tape on a cable coming from the battery on my used car I bought recently and opened it up to find this:

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Is there a hazard to the cable or components if I keep the cable like this and tape over it again?

If I should repair the cable, would it be ok to cut out the damaged part and reconnect the ends with a soldering connector tube? I fear replacing the whole cable is not an option, so if this is not a good idea, I'm open for better ones. Here to learn.

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After disconnecting the negative battery terminal, if you cut out the corroded section of wire and then make a proper solder joint -- which begins with a secure physical connection between the wires to be joined -- the resistance of the soldered cable will for all practical purposes be indistinguishable from the original wire. Yes, solder has a higher resistance than copper, but current in a properly soldered joint passes through solder for only a small fraction of a millimeter because the two wires to be joined are already physically touching. Any added resistance from solder is completely trivial.

However, soldered connections in stranded wire that are subjected to vibration and physical bending can lead to fracture of the wire through metal fatigue. If you're planning to keep the car for just a couple of years, solder should be fine in the short term. But if this car is a keeper and if this wire is subject to movement because of engine movement, a better choice would be to cut out the corroded section, then use a split bolt connector. These are especially useful for high-current applications. I've used them on heavy battery cables to connect high current loads, and they have lasted the life of the vehicle. Insulate with many layers of high quality electric tape and you'll never have a problem with it.

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You need to replace the cable as there is corrosion inside of the cable. There is no way to get rid of the corrosion, so replacement is your only option. The corrosion increases resistance going through the cable, which means it won't be as efficient as it should be. Heat can generate, which if it gets bad enough, might cause a fire. Butt welding (if that's what you want to call it) isn't a good option, either. This also creates a lot of resistance within the cable at the joint, which creates heat.

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  • This is an auxiliary battery cable, there are two fat ones for starting I presume, so I don't think that this one draws a ton of current, so maybe soldering them correctly after removing the corroded part could suffice? I really don't want to replace the whole cable, I'd probably need to take half the car apart. Sep 17 at 19:55
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    @ManuelSchweigert - Well, if it didn't draw much current, it'd be a lot smaller cable. Remember, the manufacturer only puts what they need to into a car so it will run properly. They don't over engineer things and make them better than they need to be, because it costs them money they don't need to spend. This may be the primary power source for your auxiliary stuff, like your radio, ECU, etc. If so, with the corrosion inside of the cable, it will act as a resistor and cause you problems. Sep 18 at 1:56
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    I was about to say "naaah, just put a fresh tape over it" but then you mentioned corrosion and I realized that that's what that green stuff is. So, yeah, good point. Replace it.
    – Vilx-
    Sep 18 at 22:50
  • @ManuelSchweigert Putting fresh tape over it will "fix it" until it fails. That could be tomorrow or in 10 years time, but it will probably happen somewhere inconvenient (e.g. you lose all power when you are in the fast lane on the autobahn)
    – alephzero
    Sep 18 at 23:15
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If you attempt to cut this wire for repair, disconnect battery negative first to prevent blowing a fuse or becoming an arc welder. That looks like 10 gauge wire and if there's enough slack, cutting out the corroded part, stripping back insulation and either meshing the clean ends together or use a plain butt connector crimped onto both ends of wires, solder can repair this damage. Once cut, slip a piece of heat shrink tubing over one wire far back to prevent heat from soldering hastening the tubing to shrink. Once soldered together with electrical/electronic solder and flux to keep copper from oxidizing as its soldered, let the wires cool off before slipping the heat shrink tubing over the soldered connection. Heat shrink tubing should cover insulation and soldered wires. A match, lighter or soldering iron played under tubing should start shrinking it until it forms a tight insulated cover over the repair. Soldering requires clean copper wires free of corrosion to allow flux and solder to flow like water onto copper wires, looking shiny wet when soldering. Not disturbing the connection while soldering then removing heat should turn wet shiny solder into a dull grey color as it cools and hardens. If you've never soldered, practice on wires first before making this repair. A good solder joint will carry the amperage without overheating from a poor repair. Google videos of soldering for help. Soldering wires butted together isn't recommended for 10/8/6 gauge wires. Mesh clean ends together, 3/4 to 1 inch then solder. Technique counts to ensure all wires are meshed and packed tightly before soldering. The alternative? The correct copper ferrule or thin walled tubing that fits tightly over each end then crimping each end for a mechanical bond. Try pulling this apart. If wires pull out, crimping failed. Every small gauge connector using machine crimped terminals cannot be pulled apart. The same repair to a 10/8/6 gauge must be crimped to resist pulling apart. Soldering bonds wires and ferrule into one intact unit that cannot be pulled apart.

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  • I think it's 6 or 8 gauge wire, definitely thicker than 10. The answer above seems to contradict yours, Paulster2 says that soldering the ends back together would result in a lot of resistance. What do you think? Sep 18 at 0:22
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    If you have never soldered before, this is not the right job to learn on. If nothing else, a typical soldering iron and solder meant for use on electronic circuits are completely the wrong tools for the job.
    – alephzero
    Sep 18 at 23:19
  • Review how large copper cables were once soldered in videos to splice power cables for power distribution of the electrical grids all over the world. Copper cables as thick as an arm, soldered with molten lead using acetylene torch. These cables carry several hundred volts and similar amperage. Videos are historical and presented by power companies. Soldering relatively small gauge copper wires is easy when familiar with soldering.
    – F Dryer
    Sep 19 at 0:19
  • I believe the reasons crimp connectors are preferred to solder in automotive are (i) they're reasonably easy to get right with not much practice, which I personally cannot say for soldering, and (ii) they provide good mechanical connections, something solder does not.
    – Mathieu K.
    Sep 19 at 4:21
  • With respect, can I suggest breaking this answer into paragraphs, or even lists of steps?
    – Mathieu K.
    Sep 19 at 4:22

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