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I was having intermitent loss in charging on my 92 Saab 900 convertible and when i ran the tests in the Bentley manual it seemed that the alternator had gone bad. I had the alternator rebuilt with a new voltage a regulator, brushes, and commutator (which were heavily worn). Installed it and still no charging. the exciter wire is only putting out 5.6 volts and the battery light is always dimly lit. The battery is fully charged when i made these checks. Im not sure if this could be related but the day i started having trouble with charging i installed new front 60 watt speakers.
 

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You're going to want to post this in the c900 forum a '92 is not a NG900.

The exciter wire and battery light are actually the same thing - key-switched 12v from the instrument cluster passes through the light to the alternator. When the alternator is stopped, it provides the ground and the light is on. When the alternator is moving, there is 12v on both sides of the light and it's off.

A dimly lit light suggests there is always ground present. Are you sure you connected the wires back up correctly? The oil pressure idiot light is right there, and if you confused those wires you'd get this behavior.
 

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Discussion Starter #3
You're going to want to post this in the c900 forum a '92 is not a NG900.

The exciter wire and battery light are actually the same thing - key-switched 12v from the instrument cluster passes through the light to the alternator. When the alternator is stopped, it provides the ground and the light is on. When the alternator is moving, there is 12v on both sides of the light and it's off.

A dimly lit light suggests there is always ground present. Are you sure you connected the wires back up correctly? The oil pressure idiot light is right there, and if you confused those wires you'd get this behavior.
i did not make any changes to the wiring behind the instrument cluster and it all had been working properly before
 

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Not the instrument cluster, the alternator. You said you replaced it. The oil pressure switch and alternator exciter are right next to each other.
 

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Discussion Starter #5
i had it rebuilt. Im pretty sure i didn't not cross those wires i have the green and white one going to the alternator. when they rebuilt it they sprayed the whole thing in this paint I'm thinking i may need to clean it off the connecter.
 

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One lone voltage reading doesn't mean much.
Battery voltage at rest? At alternator? When running?
Leaving your voltmeter grounded at the battery post, engine running, see if you have voltage where you shouldn't have, such as the alternator case or engine block.
That's the very basic data.
 

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Discussion Starter #7
One lone voltage reading doesn't mean much.
Battery voltage at rest? At alternator? When running?
Leaving your voltmeter grounded at the battery post, see if you have voltage where you shouldn't have, such as the alternator case or engine block.
That's the very basic data.
battery voltage at rest : 12.93 battery voltage at alternator : 12.8 battery voltage when car is running: same as at rest but decreasing. Voltage at exciter wire when unplugged from alternator tested using alternator case as ground: 11.9. Voltage of exciter wire plugged into alternator using alternator case at ground: 5.6
 

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That's probably why the alternator light is on... that is insufficient voltage. Are you certain you don't have a damaged ground wire?
 

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That does sound very much like a poor ground wire connection or a damaged ground wire .
Do you have a set of jumper leads handy ? As a simple easy test , create a substitute ground from the alternator casing to the negative terminal of the battery , if that kills the alternator light and you are close to 14V at the battery with the car running , then you know the ground is the cuplrit .
 

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Discussion Starter #10
my thinking for ruling out the ground is that when testing the battery at the alternator I'm getting the correct voltage while using the alternator case as ground.
 

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Remove gr/wt wire. Clip your test light to the + battrey terminal and touch it to the alternator Field terminal.
Now it;s your battery light.
What happens?
 
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