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  #1  
Old 21st December 2003
turningfast turningfast is offline
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Default help me please, no charge

Hello i am new to this forum. I have a 91 900 s and it won't charge. I have replaced the alternator and regulator but still won't charge. I am an auto tech but work on GM cars primarly. The battery is OK and will start the car with no problem. after the car starts though, the field will not activat. I searched the forums and am begining to wonder about two things; the diode behind the charge light and the little black device on the back of the alt. with a single wire. What is thie little box above the regulator with a single wire? After I put in the alternator the batt. light came on and turned off after I revved it. It has not come on again, when started, but still won't charge. I am thinking that mabey the diode behind the charge light failed and is causing an open causing it not to charge but have no clue on how to check it. Does the alt light circuit go to the alt. from the single wire to the back of the alt? I have no diagrams and could not find a book at several auto stores.thanks for your help. DAn
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Old 21st December 2003
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MSOEMiller MSOEMiller is offline
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The "black device" holds the brush.

You should have a positive cable connected to the starter and a black ground attached, not the one that you stated.
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Old 22nd December 2003
turningfast turningfast is offline
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OK, The "black device is not the one shown in that picture. It is not the shield around the positive conection that holds the brushes. It must be a capacitor or something. Ther is a case ground to the alt. and the pos. goes to starter. I am a tech so i checked all grounds were tight and all wires were in good shape. It's not a brush because it does not contact the armature or commutator. It's a sealed little box with one wire. There is only 2 wires connected to the alt from the harness, the red pos. wire and a black single wire connected to a tab on a terminal of the alt. Then there is a ground going to the block connected to the case of the alt. all grounds are tight and good pos connections. the solenoid seem to be fine. I put everything back the way it was so no wires are disconnected or misplaced
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Old 22nd December 2003
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gerryp gerryp is offline
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Hi turningfast

I posted something on this a while back - search on "Lazy Charge Light".

To summarise:
The excitor current runs through the charge light, if its blown the alternator won't start.

Make sure the charge light is 2 watts, not the standard 1.2 watts.

The diode stops the charge light glowing dimly when the alternator is working. Diodes don't often blow unless mistreated (cooked).

Hope this helps 8)
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Old 22nd December 2003
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gerryp gerryp is offline
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On my car the small wire going to the teminal on the alternator is white/green. But my car's an '88.
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  #6  
Old 22nd December 2003
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Here is a link to charging system wiring diagram for 91-93 model years scanned from the Bentley manual. Get one of these manuals!

In the diagram, 1 is the battery, 2 is the alternator and 4 is the starter. Connection 54 at the ignition switch is hot while in "Run" and off otherwise (including "Start").

Does the Charge warning light come on when the ignition is on with the motor not running, then go out after starting? If so, your lamp, diode and exciter circuit and field should be OK.

Do you measure almost 14V at the heavy red wire attached to the back of the alternator with the motor running? Ditto at the battery? If you get nearly 14V at the alt, but only 12V or so at the battery, check the cable from alternator to starter and the alternator ground again. Some people have had problems with iffy alternator grounds.

As shown in the diagram and gerryp mentioned before, the exciter wire is green and white.
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Old 22nd December 2003
floflo001 floflo001 is offline
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The black device is a capacitator.It is there to make sure the radio or speakers do not make a humming noise.It is also needed to take away the small voltage peaks.The regulator cannot create a perfect +12v line
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  #8  
Old 22nd December 2003
turningfast turningfast is offline
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Thank you all for the info. The diagram is a great help. I brought my good multi meter home with me from work, I don't think the piece of trash I was using was acurate when I was ohming out the grounds looking for a high resistance. I figured the black box was a capacitor or condensor, thanks floflo. If that failed It probably not cause a no charge situation, so that's of the list. Thank you all again.
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