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Charging woes

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1999 9-3 2.0L

My dad's car quit charging the other day. Today I removed the alternator and had it bench tested at local parts store. Passed all tests. Reinstalled it, still nothing. Wiring is complete from Alt to battery. Ground has continuity to battery from alt case. Running off the battery, I unhooked the pos cable at battery and it immediately died so definitely not charging.

Educate me on the idiot light wire on the alternator. It is on when running (cause it not charging obviously). Isn't this an exciter wire of sorts? Seems if it wasn't functioning correctly (blown bulb, broken wire, etc) then the light wouldn't be on at all....

I'm a fair mechanic. Just not much experience with saabs.
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Well i might try this test tomorrow but also am wondering, is it worth having the battery tested? Is it possible its simply not holding a charge? I dont have access to a multi-meter at the moment but i only checked battery voltage at idle which was 12 but didnt get a chance to rev it up and see if it rose at all. Seems like a no to me because even at idle with a bad battery i should still be seeing 14v roughly right? Unless the battery's internal resistance has risen is so high that its reading low? My boss did lend me a known good backup battery so ill go for a drive tomorrow and see if it can go a few drive cycles and still start. On my way home just now the dash lights started illuminating ABS BRAKE etc so i knew my battery had dropped low, got home and yep won't start.

As en edit i don't believe the internal resistance rising could have anything to do with the voltage at the battery when running right? When running the power you are seeing from the multimeter while connected to the battery is the power coming out of the alternator before its even had a chance to go through the circuit of the battery to lose voltage from internal resistances?
 

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If you have 12V at the alternator, that's coming from the battery connection.]
Can you explain this to me because it doesnt make any sense to me. From numerous posts ive read including one from this forums a member said "if you dont have 14V at the battery crawl under the car and while its running and between the positive terminal on the battery (with the big wire coming off it) and a good ground such as alternator casing or engine. If you dont have 14vish here its time for a new alternator."

So can you explain to me how i didn't directly measure the alternators output? I literally just watched a video too where this guy with his car running puts the positive multimeter lead on the big terminal on the alternator, that has the red wire going to the battery and alternator case as a ground. This is what i did.
 

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There are two tests...

With the car off, you should have 12v at every major junction... The battery terminals, the alternator B+ terminal, the maxi fuses.

With the car running, you should have ~14v in the same places.
 

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You did test the alternator output exactly as you said, but if the alternator is not doing anything, you will still have 12V at the big terminal on the alternator because it is connected to the battery. No output from the alternator = you are measuring battery voltage. Now if you had the big wire completely disconnected from the alternator (not a good thing to do with battery connected because if the end hits anything, you're gonna create a short) and you were still seeing 12V, then the alternator is charging some but not enough.
 

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Discussion Starter · #46 ·
Was able to get over to dad's car again today. Connected wire from battery to exciter wire on alternator with it running. No change. Still just read battery voltage. Gonna replace it. I noticed inside that the battery light on the dash is dim, not fully lit but not out either (key on engine off).
 

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Yep, 90 amp, that's what it had in it (original one). It's just a regular NA S convertible, not Turbo, not SE. The DB alternator came today. It appears to be very good quality. The box did say Made in China, but I don't know what isn't these days. It had a test sheet inside the box where they supposedly tested it. The test sheet did at least match that alternator. I already got it installed and am back in business. 14.0 V at battery, no battery light. So now I'm gonna take my old one and have it tested just for kicks. Then, because I found a brand new voltage regulator with brushes (Meyle - Made in Germany) in my stash of parts (that I didn't realize I had when I ordered the new alternator), I'm gonna install that in the old one and have it retested. If that fixes it, then I'll have a working spare just in case. My other two NA NG900s both are still on their original alternators, one is at 177K and the other at 198K.
 

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.well done ,
Was able to get over to dad's car again today. Connected wire from battery to exciter wire on alternator with it running. No change. Still just read battery voltage. Gonna replace it. I noticed inside that the battery light on the dash is dim, not fully lit but not out either (key on engine off).
Curious re the Dim battery light , that is suggesting to me that the Alternator it not well grounded , For Kicks run a jumper lead from a good earth point to the alternator body . Regardless of the condition of the alternator , that light should be bright with the key on , engine off . Check grounds and check cleanliness of connection points on the exciter wire/
 

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i've only ever replace 6 complete alternators(Slip rings were excessively worn) over my 25yrs of working on cars,rest i've have cleaned/rebuilt with just a change of regulator pack and brushes,never ever had a bosch reman fail..
 

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Something is wrong with my old original Bosch other than regulator and brushes. I took the old one and had it tested. Failed of course. Replaced regulator and brushes with new set, Tested on same machine at AZ, still failed, no charging. The regulator and brushes I took out looked okay. The brushes were worn some but still making full contact. So something somewhere else inside has failed, maybe slip rings?
 

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I had a bosch unit fail because of bad diodes inside but it did still charge it was just when the car wasn't running it caused a draw on the battery.. Not sure what else it could be. I really wouldnt trust autozone too much tho
 

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So doing some troubleshooting on the failed alternator and im 99 percent sure i found out the problem.

Testing the resistance of the brushes one has low resistance (1 ohm roughly) and the bottom brush had 14,000 ohms of resistance. So where the brush connects to the pigtail or somewhere else internal to the brush/regulator is causing extremely high resistance which is to much opposition to current flow to turn the dash light on.

Good news is a brush/regulator is only 10$ plus shipping so i should have a backup alternator!
 

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These days, bad brushes seem to be the most likely culpritfor a bad alternator, followed by bad regulator (especially if the electrical system has been abused), and then bearings.

I haven't actually heard of the windings failing. Well, maybe if you always run the engine to redline, that might cause damage, as the alternator spins, what, 1.5x or 2x engine speed.
 
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