Alternator question

I was driving home from a basketball game over the weekend and I noticed my dashboard lights fading in and out. Then, about 10 mins later my battery light went on. It stayed on about 10 mins, then turned off for about 10 mins, then stayed on for another 20 mins until I got off the highway, at which point the battery light went off again. I went to Autozone the next day, about 10 mins from my house and my light never went on. At Autozone, they said that everything was fine. My battery carried a charge of 14.4v, and the indicator read “good” on the alternator. The next day, I took the highway to my Saab mechanic to get my oil changed and the battery light went on once, and the mechanic said that everything looked fine (but I don’t think he checked). The battery light went on once again when I went home. The next day, I went to NTB and they said that my alternator was failing at the higher RPMs which is why the battery light went on at higher speeds.

Is this possible? I thought the alternator either worked or it didn’t. The charge on the battery is still 14.4 according to NTB. My fiancee’s dad said that the belt could be slipping, but it doesn’t look bad/cracked. Is a rebuilt alternator just as good as a new one? Some of the ones I have looked at look as expensive as the new ones. I’m not looking forward to replacing this one.

I’m not sure what would be causing your problem, but I wouldn’t buy a rebuilt alternator, I hear they are often junkyard pulls that have just been cleaned up. I wouldn’t even buy a new alternator at Advance Auto, not sure about AutoZone. I’d buy a NAPA or a factory one.

It could always be a wiring problem. Replacing the ends on your battery cables is a cheap thing to try.

That’s generally true, other than when there’s diode failure. But in your case, it sounds like it works, and then it doesn’t, then it does, then it doesn’t…

It’s quite possible that the alternator brushes have worn to where they no longer make consistent contact. If this is the case, it may go back and forth between charging and not charging (for a little while yet) before finally quitting altogether. Testing it while it’s charging only reveals that yep, it works when it works. It’s the fact that it doesn’t always work that is significant. Your choice is to wait until it fails during testing to confirm that it is the alternator, or to play the odds (95+%) and replace the alternator now.

There are good rebuilt alternators, and there are crap ones. In my area, I’ve had very good experience with the Ultima line from O’Reilly Auto Parts, and the top line from Carquest. I would also expect any OEM (dealer) brand to be good.

Before replacing an alternator check the wiring. Make sure the battery terminals are tight and not corroded. Then push and pull on the wires that go to the alternator if one of them is loose, you have found your problem. Before fixing any wiring disconnect the negative battery cable. Also check to see if your alternator has a fuse. If it does check to see if its contacts are clean. Always check the cheap easy stuff first.

How many miles on this car?

Alternators are used in cars because they do NOT have brushes. Generators have brushes, and are DC devices. Alternators have no brushes, and are AC devices, typically three-phase to minimize ripple, and feed into a rectifier to produce the DC.

Typical electrical fade problems as described usually resolve down to cable connections (not just where they bolt down, but the actual crimps as well), or are heat related. An automotive regulator can shut down on heat, then cool off and come alive again. That can be either a faulty regulator, or poor mounting to the vehicle frame, preventing it from dissipating heat properly.

I can see you’ve never overhauled an alternator. I have. Alternators have brushes. Illustrations here and here.

You a mistaken. Here is an alternator testing video that will correct your understanding of alternators.

To the OP, if you are having very regular intermittent problems, I would if it were my vehicle, put in an additional ground cable from battery to engine and test run that for a couple days, then if that test is unremarkable, another test from ground post to frame.
Someone else posted to check connections from BAT wire back to battery including any fuse that may be present.

It has 150,000 miles. Thankfully, I have another car that I can use, because just getting to the alternator is a pain the ass. I’ve checked the tensioner by pulling on it and looking for slack. I’m not sure how to check a tensioner otherwise. I’ve disconnected, cleaned and reconnected the battery posts (they weren’t really that dirty), but following those to the alternator doesn’t get me very far. I’ve also ran a load on the battery with the testing gadget thing I borrowed from my neighbor and he says my battery is good. I’m not sure there is a fuse, I’ll have to call the mechanic. He quoted me $600 (estimate) to fix it and NTB quoted me $770 all-in. It’s seems like a lot for a car so old (then again, I haven’t had a car payment in 6 years…)

I was talking to the COO of a division I support and he says he changes alternators all the time and that they’re really easy. Of course, he drives a 1990 Crown Vic (though, I do admit it looks impeccable, even in all this snow).

What test was autozone running, as compared to NTB? Can either of those tests be wrong? NTB said failure was imminent, even though my battery still shows full charge.

Really? Huh, I never heard of that before… The alternator seems to be bolted in really tight. IIRC, the bolts are huge.

Ok, I’m not sure what you’re talking about here. Apologies in advance for the amount of ignorance this post will contain.

Are you saying that I should run a wire with an alligator clip from the posts to the spark plug/direct ignition assembly thing? Will I need a gadget to then test the alternator? If so, will the one from autozone work? If that is inconclusive, then I should run the same wire from the negative terminal to a random part of the engine frame, yes? Thanks.

Old doesn’t have that much to do with the price. Being a Saab has a lot to do with it.

They are really easy – on some cars. Some people just don’t seem to grasp that not all cars are designed the same. Again, its being a Saab has a lot to do with how easy or hard a job it is.

They probably did the same tests. And it was probably working perfectly when Autozone tested it, but that doesn’t mean it doesn’t have a problem – it just means the problem wasn’t evident at the time they were testing it. NTB may have seen the alternator cut out briefly.

Now, I know I’m speculating here. I haven’t seen the car, and I haven’t tested it. But I’ve been repairing cars professionally for over 35 years, and I’ve seen a lot of alternator problems. What you’ve related is pretty much a textbook case of how many alternators act when the brushes are at the tipping point of worn out. They make contact (barely, but that’s all it takes) and the alternator charges; you hit a bump (or whatever) and they lose contact and charging stops; hit another bump and they make contact again. For the back and forth charging/not charging you’ve described, worn brushes is by far the most likely explanation. I expect that pretty soon the wear will be enough that it will stop charging, period. At that point it can be tested and the cause can be confirmed. But it’s a very good bet that a faulty alternator will the determination. Some of the other suggestions here are within the realm of possibility, but they’re in the 1% range of probability. Worn brushes is in the 95+% range of probability.

That’s because it’s in the <.001% range of probability.



But you’re not experiencing what I would call a “very regular” intermittent problem. Rather, it’s a very recent problem. Worn brushes are much more likely than a faulty ground. Can’t hurt to test it this way, but don’t get your hopes up.

I had a somewhat similar problem years ago and it turned out the problem was the voltage regulator, not the alternator. You may want to check that out.

Sometimes the spring in the tensioner can get sticky and cause intermittent charging, I just went through this with my 2000 Blazer. I took it off and sprayed it with WD-40 and worked it back and forth until it loosed up and returned to its tension position by itself, no problems since.

The best test for an alternator is out of the vehicle and they attach it to the test rig. Then they can verify at different RPM’s. Either way I am going to side with Gary T on his determination of the brushes going out. I have seen this on drills where at low speed the drill will work and as I approach max it starts to fail. Upon inspection the brushes were worn down to the point that the spring tension was unable to keep them on the commutator contacts at high speed and was probably skipping. Therefore breaking the connection.

As for the cost of replacement that sounds about right for a SAAB. That’s why I got rid of mine. Too much in repairs. Also, I have never heard of a “new” alternator for replacement. They are only new on a new car. After that they are rebuilt/re-manufactured. IIRC, the typical part cost, with turning in the old one, is in the range of $250 to $350 depending on the vehicle. Then there is the labor. But, I can’t see more than two hours if it’s your first time replacing one.

You can call the dealer and ask them what the cost of a new alternator is and then call around to AutoZone, PepBoys, etc. It’s probably a Bosch but if it’s a late model SAAB it will have more than likely pulled from the GM parts bin and maybe be an AC/Delco brand. Which I think would max out at $250. But, I could be wrong. It’s been awhile since I replaced mine.


My apologies, I worded that very poorly. What I related that I might do was connect another ground wire (black # 8 <> wire with alligator clamps ) to the negative battery post and to a good solid ground on the engine block, base bolt of alternator would be good as long as no part of this jumper could touch a positive connection or come loose and get tangled in the belts or fan. This is just a ground continuity rule out test.
I agree with Mr. Gary T, he is much more experienced in this area.

I had a costumer last week with a very similar problem. His lights would dim and brighten and a “ON” vehicle test didn’t pick up anything indicating his alternator was defective. i also did not have a bracket to do a bench test on said alternator.
I modified the (ford escort) bracket to also work with this one and customer came in with his core. I did a sampling bench test and a full field stall test on the core and all looked good. I then put the reman on the test bench and it failed the test!
“NOW WHAT”, so i sent him home with the reman and his core (I know this customer very well)(I know 95% of the customers that walk through the door):wink:
He installed the reman, This alternator would load and almost pull his engine to a stall and unload, back and forth every 10-12 sec.
He removed this reman and reinstalled his old (referred to as a core) and I again put the reman on the test bench and it failed again, then I asked the store owner to help me. It passed then:smack:, but then failed differently right after when retesting.
That reman went back with a defective sticker and have not heard from customer yet, but will if I have to run him down on the lake.

Used to be that way, but over the last several years some alternators and starters have been available new in the aftermarket.

CarQuest has New -Or- Re-manufactured in almost all application. We even have some Re-built starters and alternators that we don’t carry in stock but are next day in most application. They are lower cost, and very limited warranty. The owner said to keep in line price wise to o-riley’s.
Funny part about new components, there are no cores.

really? Then what am I paying for? Is there any real difference then in a rebuilt versus a new alternator (I know I’m showing my ignorance of alternators here)? What about parts stores? Every dude around here where I live says to go to Napa, but I like O’Reilly’s lifetime warranty. Pep Boys also has a new part, but no price listed, so I guess that’s another thing to ask about, like if a core is included.