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Alternator - Burnt line

After driving a good distance the car was stopped and in park for about 10 minutes running when all of a sudden there was a burning smell. After that the battery light came on. We checked and couldn’t find anything and the burning smell was going away. Then we drove the car back, without issue, with the battery light on. I searched for a while and discovered a direct heavy wire connection to the alternator was burnt. I spoke with some people and they said the alternator may still be good and that a positive wire to the battery might have shorted. The wire is burnt so bad I can’t even tell if it was a red wire.

Later, I charged the battery to full and took the car to the parts store. They tested and found there wasn’t any voltage coming from the alternator and the battery is good.

I put the alternator in a year earlier and it was no easy task. I had to take many things off to get to it including the engine mount and shifting the engine to the front.

Any suggestions of what I should do or try would help.

How did they test the alternator? If it was from the battery posts, the test isn’t valid because of that fried connection. My guess is that the connection started to burn because corrosion increased the resistance at that spot. Repair the connection and test the alternator again.


They tested the alternator at the battery posts.

What you’re saying about the corrosion makes sense. More current than the corroded connection would allow thus heating up.

I’m not sure how I would go about fixing the wire. Is there a pigtail or connection that I can purchase?

It should use a standard ring connector. You will have to cut the wire back until you get past the damaged area.

That connection was loose for a while to burn up like that. The corrosion is is a result of the heat, loose alternator connections burn up like that is the desert as well.

It is doubt full you will be able to clean up the alternator post to restore the connection, sometimes the stud is so brittle from the heat it breaks off when trying to loosen the nut. You will probably have to cut off and replace about 6" of that damaged cable or install a new cable from the alternator to the battery junction.

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You can’t tell it from looking at the picture but the wire is completely disconnected from the ring connector. The connector doesn’t seem to be loose at all. I suspect the wire may have had some strands broken when the alternator was put in a year ago and eventually wasn’t able to carry the amperage. One question I have is when putting in an alternator should you use electrical grease when connecting this alternator wire?

I just got into a discussion about how you put the connector on the cable. I just watched a video about this specific type of situation where they soldered the wire on. Other people tell me to crimp it on and never use solder because the vibrations will cause it to brake. What is the proper method?

In any case I wouldn’t be able to solder a connector on the wire on because it’s too buried between the engine and firewall. It would probably be a struggle to crimp on connector on because of the tight space and I don’t think I could take more than a couple of inches off the wire because it’ll be too short.

I’m leery about putting a complete new wire from the alternator to the battery because if it’s not done right the car could go up in flames.

Any thoughts on the alternator? I’m told by several people the alternator will most likely be fine and still work. Should I try to use it or get a new one? I was going to avoid replacing the alternator, if it still runs, because of the amount of work (or labor cost) to put a new one in.

I’m open to any suggestions?

I’d be more leery of a patch job. Get a factory replacement wire.

If the diodes are toasted in the alternator a new wire will burn as soon as it is connected. The alternator needs to be removed, opened and thoroughly inspected before connecting it. A dead short to ground on a charged battery can cause an explosion.

[quote=“Rod_Knox, post:8, topic:95345, full:true”]
If the diodes are toasted in the alternator a new wire will burn as soon as it is connected. The alternator needs to be removed, opened and thoroughly inspected before connecting it. A dead short to ground on a charged battery can cause an explosion.
[/quote]The alternator can be tested for shorted diodes without dismantling it.

And if I connect my DVOM red lead to the BAT terminal and my black lead to the alternator housing with a result being ZERO ohms resistance what then? The BAT connector has a two piece plastic bushing insulator that could be shorting to the housing. Will ZERO ohms give any insight into that situation?

For the average DIYer that alternator is now a core.

If you’re thinking about replacing the alternator, one idea, remove it and take it to an auto parts store that has an alternator test fixture. They’ll usually test it for a small fee, sometime gratis. The burned wire doesn’t mean the alternator is bad. Not at all in fact. I wouldn’t make that assumption and just replace the alternator. One reason, the replacement alternator may not be as good as the one you currently have. Why take that risk?

Replacing those big thick wires can often be beyond a diy’ers fix job. Too many things can go wrong. That wire carries hundreds of amps, so the connections all along the way have to be perfect, otherwise you’ll be quickly back in the same boat. New, and burned wiring. Suggest to ask a shop that specializes in auto-electric work to do this repair job for you.

Update: We ended up taking the car to our mechanic and he fixed it for around $100. I think this is a very good price considering how much work there was putting in the alternator. The alternator was good. He put a new connector on the wire. It doesn’t look like he took much wire off if any. It looks like he took the entire post off and used a screw, were the post was connected, to connect the wire. We have been driving the car and it seems to be working fine now. One concern I have is if we ever had to get a new alternator the connector wouldn’t fit on it since he used a smaller connector on the wire than it originally came with. I’m not sure if it matters but on the original connection there was a piece of rubber covering the connection and now it’s exposed?

That may have been a stud that screwed into the original alternator, and he just removed the stud and attached the wire to the alternator using a bolt or screw of the same dimensions and thread pitch of the stud. I don’t see why that wouldn’t work as well as the stud method. The only problem you might run into is that if that connection fails and overheats the screw, it might be more difficult to fix since the heating point will be closer to the alternator case; i.e. you can’t just replace the stud, b/c the stud isn’t there any more.

If you ever need to replace the alternator in the future, the connector problem – if there is one – can be solved inexpensively at that point. I wouldn’t lose any sleep over that.

If I were making the new connection from the wire to the ring-connector, I’d both crimp and solder it. That’s a more robust method than just crimping it. If you don’t see any solder, you might take it back and ask him to solder it for you. Shouldn’t be much of a fee for that.

The rubber over that connector is there mostly to prevent someone who’s working in the vehicle engine compartment from accidentally bridging that point to the chassis with a metal tool, like a screwdriver. That would create an inadvertent direct short circuit from the battery positive* to battery ground, and could burn or otherwise injure the person holding the screwdriver, let alone the problem of sparks mixing with any gasoline vapors in the vicinity. Even a slight possibility the alternator or other electrical circuitry in the car (like the engine computer) could get damaged itself if that happened.

There’s usually a rubber gadget over the battery positive post for the same reason. Suggest to improvise something if possible for both the safety of whoever’s working on the car, and for the car’s electrical system, even if it just wrapping some electrical tape (Scotch Super 33+ preferred). Most repair shops keep various rubber gadgets like that they’ve removed from other cars on-hand too to fix this kind of problem when it crops up, so asking your shop to improve that is another option. Asking an auto parts place for ideas is another option. Replacing the screw w/a new stud so it is like it was when new, yet another option.

  • The big alternator post connects directly to the battery positive via that thick wire, sometimes without any fuses, but often there’d be at least a fusible link in that circuit which would offer a modicum of protection against an accidental short.

It looks like a bad crimp at the ring connector. They get corroded, overheat and burn.