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Discussion Starter #1
1993 Saab 900C Convertible:

My alternator is not producing enough voltage at idle. Expected 14.2v-14.7volts.
My results: 11.99 volts.
I read that a functional Battery Lamp was required to properly charge the battery.

I read that the dashboard Battery Warning Light / Lamp should illuminate in the ON position , and then go out when the engine starts.
I see no Battery Warning Light/ Lamp as I turn the key to ON, nor as the engine cranks, nor as the engine starts.

I suspect a failure of either the bulb or the supply of 12v to the lamp bulb.
At least that could be a component of my issue of : battery not receiving enough charge.

How do I access the lamp bulb?
The Bentley manual says that it is located at location 47E in the dash , but I do not know if the entire needs to be pulled out.
Anyone done this replacement job?
 

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Start first by grounding the exciter wire at the alternator and turning the key on. If the light turns on, it's not the light but the alternator.
 

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Discussion Starter #3
Will you kindly educate me some more?
I Googled alternator exciter wire and learned that if an alternator was on the shelf a long time , it will lose its internal magnetism and consequently fail to generate a charge to the battery. Never knew that.

You suggested to ground the Exciter Wire at the alternator.
Which of the many alternator terminals is the exciter wire?

Once I find it, I will merely create a jumper from any chassis ground to the Exciter wire?? -- and that will create the alternator's internal magnetism ??

If I follow you correctly, that ground will differentiate lamp bulb vs. alternator.
I suspect that because the lamp does not light on the dash and at the same time I am not getting sufficient charge to the battery, that my lamp bulb is blown .
That is why I inquired about how to replace the dash battery lamp light bulb with the special 2 watt bulb.

Any links to reading material / schematics will be helpful.
I have the Bentley's manual but did not see EXCITER WIRE.

Thank you for any input.
 

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Unplug the little green/white wire on the back of the alternator and ground it. Look for the light on the dashboard that cannot light unless a ground is provided at the alternator end. Do not assume the alternator case is grounded, check it.
When it starts charging, that terminal gets 12v and the light on the dash loses its ground and goes out.

Stop thinking of electricity as only 12v. All things electrical need a complete circuit. The ground side of the circuit is just as important as the positive side. (Your A/C relay pull-down circuit has 3 switches on the + side and 2 on the - side.)
Find general explanations of electrical functions in section 3.1 of the factory service manuals found in the stickies.
 

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Discussion Starter #5
Thank you , Gentlemen.
Now , I believe that I understand the circuit. I did some outside reading which reinforced your comments.
The Battery/Alternator lamp will receive 2 wires.
One wire receives 12v from positive battery terminal.
The lamp needs the second wire to serve as a ground to allow the current to flow from positive supply from Battery (+) terminal through the lamp and then through the green/white wire.
Before then alternator starts to turn and generate a counter current from alternator terminal D+, the alternator D+ terminal should be serving as a ground. Hence, if bulb is good, the dash battery warning lamp icon should glow.
Once the alternator starts to turn and generate a counter current into the green/white wire, the counter current will zero out any current against the incoming current from the battery B+ supply.
Thank you for showing me the way.
I plan to ground the green wire and turn key to ON.
Then, hope that I see a glowing battery icon in the dash .
If glows, then bulb is good. I must look for issues in alternator ground or corrosion at connections or broken wiring.
If no glow, then replace 2 watt bulb.
 

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Be careful when you replace those bulbs. They are connected via thin foil on the back of the instrument cluster. That foil will scrape away when you turn the bulb sockets. Fixing the torn foil is a big hassle.
 

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Discussion Starter #8
Thank you for the warning regarding bulb replacement.

Do I need to pull the entire dash to access a Battery Icon Warning light bulb?
Can I reach through the radio area?

Previously, I had to reattach the heater valve control rod to the inside dash holder via slightly pulling outward on the dash after removing the 4 dash long bolt screws.
It was a pain to wiggle into the little area.
Is this the same access route?
 

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Remove the left side speaker and you can reach inside. You can look around with a mirror first to see what the connectors and foil look like. By the way, when you remove that speaker, you can reconnect the heater control rod quite easily.
 

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Once the alternator starts to turn and generate a counter current into the green/white wire, the counter current will zero out any current against the incoming current from the battery B+ supply.
One clarification: voltage is not the same as current.
There is equal voltage (pressure) on both sides of the charge light bulb so there is no current (flow of electricity) and the bulb is out..
When there is more pressure (voltage) on one side of a circuit than another, there will be a flow (current) of electricity that would light the bulb. The total amount of electricity (watts) that flows depends on voltage and resistance to the flow.
 

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Discussion Starter #11
Resolved.
My vehicle was missing the last 4 inches of the green/white Exciter wire.
Due to the education from this group, I searched for the remnants of the green/white wire, spliced in some additional length and connected it to the D+ alternator terminal. That did it. Thanks to all who contributed. I still do not get the full 14.2-14.7 alternator output. Rather, I get 13.6 volts at idle. Perhaps a poor connection at a ground? Happy that it should now charge.
 

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...the full 14.2-14.7...
I don't know where you got those numbers, but forget them. That's overcharging, you'll never see that from a working Bosch voltage regulator. 13.6 at idle is great. You should maintain that at 2500 rpm with every electrical device in the car ON.
Some GM vehicles charge that high, few others.
 
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