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  #1  
Old 05-01-2012, 12:43 PM
chetwesley's Avatar
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Alternator not working - shouldn't battery light come on?

Yesterday I got out of work and discovered my battery wouldn't turn my starter.

Got a jump from someone and then drove home, lights were totally dim by the time I got back.

The battery light never came on on the dash though. It has in the past when I had intermittent alt problems from a loose belt.

Also, yesterday before all this I found that my radiator cap had failed and was leaking coolant under the hood.

Is there a good chance that the coolant could have fried my alternator? It was just replaced this past summer, so seems a bit odd to happen now, also seems like too much of a coincidence that both things would happen at once.

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  #2  
Old 05-01-2012, 12:59 PM
rrgrassi's Avatar
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There is a certain "low" threshold before the alt light comes on. It can also be burned out.

Check your voltage regulator and make sure all connections are clean.

A coolant leak can cause problems for the alternator, if it gets totally soaked and saturated with water and coolant.

How old is the battery? Also, was the battery electrolyte level properly maintained? Low levels will kill a battery.
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  #3  
Old 05-01-2012, 01:08 PM
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Quote:
Originally Posted by rrgrassi View Post
There is a certain "low" threshold before the alt light comes on. It can also be burned out.

Check your voltage regulator and make sure all connections are clean.

A coolant leak can cause problems for the alternator, if it gets totally soaked and saturated with water and coolant.

How old is the battery? Also, was the battery electrolyte level properly maintained? Low levels will kill a battery.
Battery is only a year old or so. The alternator definitely is not working because it would not charge the battery in a 1 hr drive. By the time I got home, the lights were VERY dim, barely on. Seems like the battery light should come on by that point. Also I have seen the battery light come on before, so it would be strange for it to burn out while it is not being used.

The battery charges with a charger.

Is the voltage regulator the most likely thing in an alternator to get "fried" by a short? I've replaced that before, it is a 5 minute job.
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  #4  
Old 05-01-2012, 01:14 PM
rrgrassi's Avatar
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That, or the windings. Usually the voltage regulator is the first to go.
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70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K
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  #5  
Old 05-01-2012, 02:53 PM
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Charge up your Battery and turn the Key to the position where all of the Warning Lights light up. If the No Charging Light does not Light up it could be the Bulb is burned out or there is an issue with the ground in the Instrument Cluster.

If the Bulb is burned out your Alternator will not charge because the Bulb is part of the circuit that causes the initial excitation to start charging.

A few Members have said that when one of the Brushes on the Voltage Regulator was worn too short their No Charging Light never came on and they did not know the Battery was discharging.
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  #6  
Old 05-01-2012, 04:52 PM
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Thanks, I will check to see if the bulb comes on when I glow it.
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  #7  
Old 05-01-2012, 05:17 PM
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Why not run down to your nearest Autozone, Pep Boys, etc and have them test it for free?

John
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  #8  
Old 05-01-2012, 05:39 PM
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Test the alternator or the battery?

I know the battery is fine, it charges with a charger and holds a charge, and I know that the alternator is not charging the battery, so it is unlikely that there is a charge from it on the battery terminals.

Don't they need to take the alternator out to test it on it's own?
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  #9  
Old 05-01-2012, 09:08 PM
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I had exact same symptoms last summer and a new regulator fixed it.
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  #10  
Old 05-01-2012, 09:16 PM
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Quote:
Originally Posted by chetwesley View Post
Test the alternator or the battery?

I know the battery is fine, it charges with a charger and holds a charge, and I know that the alternator is not charging the battery, so it is unlikely that there is a charge from it on the battery terminals.

Don't they need to take the alternator out to test it on it's own?
Follow Diesel911's advice first.

Start simple. Although removing the alternator is not difficult, it is more time consuming then checking a bulb and putting a voltmeter on the battery while running.

1- So check the bulb on the cluster first.

2- If it is not burnt out, then start it and put a voltmeter on the battery terminals. It should read at least in the 13 volt range. If it is 12 something or less then the charging system is not functioning. It could be due to a loose belt, worn brushes on the voltage regulator, bad diodes in the alternator, or the wiring/connections.
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  #11  
Old 05-01-2012, 09:58 PM
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Quote:
Originally Posted by chetwesley View Post
Yesterday I got out of work and discovered my battery wouldn't turn my starter.

Got a jump from someone and then drove home, lights were totally dim by the time I got back.

The battery light never came on on the dash though. It has in the past when I had intermittent alt problems from a loose belt.

Also, yesterday before all this I found that my radiator cap had failed and was leaking coolant under the hood.

Is there a good chance that the coolant could have fried my alternator? It was just replaced this past summer, so seems a bit odd to happen now, also seems like too much of a coincidence that both things would happen at once.
the alt light is generally to alert you that the engine has stalled, or the alt belt has broken... there is not usually a light that the water pump has stopped...
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  #12  
Old 05-02-2012, 01:00 AM
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Anyone know if you have to pull out the whole instrument cluster to get at that light? I have been back there before I think, but now I can't remember the whole deal.
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  #13  
Old 05-02-2012, 01:55 AM
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Quote:
Originally Posted by Diesel911 View Post
If the Bulb is burned out your Alternator will not charge because the Bulb is part of the circuit that causes the initial excitation to start charging.

.
this is still the most bizarre thing about these cars to me. i really mean it. for all the over-engineered simplicity.. this just kills me
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  #14  
Old 05-02-2012, 01:56 AM
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Yes, you do have to pull the cluster to get at the bulb (not that big a deal in W123). However, the real issue which I don't think that you've answered is, does the light come on when you rotate the key to the first position before engaging the starter? That's when all of your warning lights are tested.

Kurt
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  #15  
Old 05-02-2012, 02:11 AM
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check to make sure the glow plug relay isnt stuck on.

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