In over 40 years of driving and owning cars I’ve never had something like this happen.
2008 Jeep. 60K miles. Battery has only been replaced once. Terminals and such were always maintained.
Recently had a problem starting and keeping it running. Found out the the positive cable had a short in it.
Only cost $32 to fix. But what causes this? The cables never move (except for once when the battery was replaced 2 years ago). So there was no movement or twisting that should have caused this. Usually when other electrical type cables and wires get shorts it’s from repeated movement and/or twisting, plugging/unplugging, etc…
Sure it wasn’t an open circuit? A short would, at best make a fuse pop and potentially explode and/or cause a fire.
It it was open, it was probably just due to time and movement and maybe some bad luck with a funny angle or a pull. The cable is its most sturdy fresh from the factory. The cable does move with the vehicle and, especially, during starting. Every bend back and forth, through hot and cold weather may cause tiny fractures. If there is anything corrosive, the process moves more quickly. As these accumulate, individual strands of copper snap one by one and, eventually, the cable fails.
I agree that ten years seems like a pretty short lifespan for this sort of thing.
A short in the cable is actually what you want, that means it is working. Perhaps it was a short to ground which is not good, or a open, which is a lot better then the short to ground, but you are still not going anywhere.
From the cost I would assume that the positive terminal separated from the wire (which is a open, not a short). Sounds like a defect.
The vehicle would start by wiggling the red cable in the middle, indicating some kind disconnection of the wires inside. Problem is, once started it wouldn’t always stay started once those wires moved again.
I have never, ever had a car battery cord do this, and I’ve owned a lot of cars including several with mileage above 200K.
That sounds like a cable problem, but not a short. One problem I have had in the past is corrosion in the cable. If you still have the old cable you could examine it, measure continuity and resistance, and even remove the insulation to see the condition of the conductor.
So it was failing open. Copper is pretty soft, and the middle of that wire gets some flex due to engine vibration. Flexing leads to metal fatigue, and cracks. That doesn’t have to be a problem due to the multi-strand nature of the cable, but a bit of moisture in the cable plus some starter current causing arcing across the cracks, and you can get oxidation and corrosion that eats out the copper causing the intermittent open circuit.
A “short” is effectively a shortcut - to earth or between the positive and negative side of a battery. It will always generate heat, sometimes spectacularly. Fuses are there in the circuit to prevent damage.
There is a reason why the battery is connected to the engine by flexible cables - the engine is mounted on springy mountings because it moves quite a lot when you are driving. Inertia makes it rotate whenever you rev it as you can easily see if you look when someone else ‘blips’ the throttle.
I highly doubt there was a failure somewhere in the middle of the wire length. Unless the wire insulation is breached, oxidation/corrosion is very unlikely to occur. And I have never heard of a stranded wire failing “in the middle of the wire length” simply due to vibration. The most common failure mode “in the middle of the wire length” is a short to the chassis due to chafing & vibration. But it doesn’t sound like that occurred here.
If the problem fixed itself by wiggling the wire, I am 99.97% confident the problem is at one of the terminations; vibration caused an intermittent open to occur where the wire terminates into the battery connector, or at the termination at the other end of the wire.
Certainly. The heavy wire is not going to be separated in the middle, connect from a little wiggling, and then deliver enough current to work. And I’ve had the loose terminal connection before and it’s just as the OP describes.
In layman’s language every electrical problem is called a ‘short’.
My wife also uses the term “short” to indicate an electrical problem of any type, typically like from a broken wire. I’ve stopped trying to correct her.
I’m sure there are people who use “short” for any kind of electrical problem, but I’ve never heard or seen anyone use it for a bad connection/break before.
I had a short in a positive battery cable once. It was on a '67 Malibu I bought for $60 and had just finished reassembling. The cable touched the exhaust manifold, its insulation melted, the wires inside made a short circuit with the engine, and the insulation caught fire. Fortunately I was able to yank the cable off of the manifold and stop the fire- a new cable re-routed and held back from the engine with a bit of coat hanger wire fixed that problem. Yep, a true short on a car’s battery cable will cause some huge problems.
My dad witnessed a mechanic that was doing something with a screwdriver near a battery. The screwdriver slipped and touched one post on the battery; his hand slipped and the wedding ring completed the patch from the screwdriver shaft to the other pole. Everything was spot welded together for a few seconds until a quick thinker whacked everything loose with a hammer.
It’s not necessarily the cable that’s bad. I had an old Chevy Monte Carlo that had a loose connector on the starter. If you jiggled the battery cable, the starter connection would wiggle and something inside the starter would short the battery connection to the solenoid connection, causing the starter to engage, which was a bit exciting to have the car suddenly start itself while you were under the car at the time, trying to figure out what was going on.
As was noted upthread, it’s pretty rare (though not unheard of) for a cable to go bad in the middle. Usually it breaks at one end or the other, or the thing it is attached to breaks.
It is possible for the cable to break in the middle, but corrosion is usually the main culprit, and unless the insulation on the wire is damaged, the middle of the wire is usually not exposed to the air or the elements and doesn’t corrode as easily.
It’s also possible that there was a manufacturing defect or someone massively kinked or squished the cable at some point. This could create a weak spot in the cable that deteriorated over time.