ALTERNATOR NOT CHARGING BATTERY

  • Tiny
  • DSquare63
  • 1998 Mercury Sable
  • 6 CYL
  • FWD
  • automatic
  • 110 miles

We've replaced the alternator and ground wires - will not charge battery?

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Wednesday, December 29th, 2010 AT 6:57 PM

16 Replies

  • Tiny
  • KHLow2008
  • Expert
  • 41,994 posts

Did you test the replacement alternator?
There are no guarantee used or reman alternators wuld be good.

At the alternator main mast, test for battery voltage. If voltage is not present or much lower than battery voltage, the connection between battery and alternator is bad.

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Wednesday, December 29th, 2010 AT 7:38 PM
  • Tiny
  • DSquare63
  • Member

We have already checked the alternator - it is brand new. We have also checked the battery voltage connection.

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Wednesday, December 29th, 2010 AT 7:45 PM
  • Tiny
  • KHLow2008
  • Expert
  • 41,994 posts

Attached is a schematic of the charging system.

The followng must be hot at all times :

1. Yellow/White wire.
2. Orange/Light Blue wire. (Disconnect to test)

Is the charge indicator light showing when igniton switch is turned on?
Does charge indicator light turn off when engine is started?
What is the voltage at B+ (Yellow/White wire) when engine is not running?
What is the voltage at B+ (Yellow/White wire) when engine is running?
What is the voltage between battery terminals when engine is not running?
What is the voltage between battery terminals when engine is running?

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Thursday, December 30th, 2010 AT 1:13 PM
  • Tiny
  • DSquare63
  • Member

Yes the light is on with key and runnin. Both wires are hot. And the voltage on all those questions is not running it is about 12.4 when you start it drops to about 10.6 and as it runs it drops

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Saturday, January 1st, 2011 AT 9:26 PM
  • Tiny
  • KHLow2008
  • Expert
  • 41,994 posts

Check the crank pully harmonic damper. If you have abnormal belting noises and the pulley on which the alternator drive belt is seated on seems to be wavy, the damper could be bad resulting in the alternator running at a lowe r than required speed due to slipping.

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Sunday, January 2nd, 2011 AT 3:06 AM
  • Tiny
  • DSquare63
  • Member

That all looks good voltage doest go up either if you raise it up off of idle.I got it to charge 1 when I re did all the ground wire it jumped to 15.3 volts turned on headlights fine turned on rear defrost and it quit and I cant get it to do anything now

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Sunday, January 2nd, 2011 AT 3:17 AM
  • Tiny
  • KHLow2008
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  • 41,994 posts

Have the battery recharged and retest.

When charging voltage drops, it could mean the alternator is not turning at the required speed or it is bad.

Check for blown fuses.

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Sunday, January 2nd, 2011 AT 4:55 AM
  • Tiny
  • DSquare63
  • Member

All fuses look goods I will charge battery and do load test it would be nice if it was that but if u run the car till it dies from low voltage if u let sit for as while battery will chagre it self back up

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Sunday, January 2nd, 2011 AT 5:11 PM
  • Tiny
  • KHLow2008
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Yes, that indicates the charging system is at fault.

Have you confirmed the crankpully is good?

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Sunday, January 2nd, 2011 AT 5:20 PM
  • Tiny
  • DSquare63
  • Member

No I havent what just runn it and give it a visiual inspection spining

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Sunday, January 2nd, 2011 AT 6:34 PM

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