Batteri not charging

Tiny
KENDRA_SCHAEFER
  • MEMBER
  • 1990 PLYMOUTH ACCLAIM
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 130,000 MILES
Alternator wont charge the batteri both the batteri and the alternator have been tested and they are both good. Its not the voltage regulator because thats built into the computer. What could it be?
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Saturday, November 13th, 2010 AT 8:34 PM

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Tiny
CARADIODOC
  • EXPERT
You're wrong about the voltage regulator. Just because it's built into the computer doesn't mean it can't fail, ... However, ... They don't fail very often.

The number one cause of a no-charge condition is worn brushes inside the alternator. The second most common cause is a break in the green wire going from the alternator to the computer / regulator in pin 20, (top row of pins, closest to the rear of the vehicle). Both of these can be intermittent so the alternator must be tested while the problem is occurring. The brushes can be replaced without removing the alternator from the engine. I've done it many times on Spirits and Shadows when installing "bugs" for my students to troubleshoot. (This applies to the little silver Nippensenso alternators.

The place to start is by measuring the voltages on the two small terminal nuts on the back of the alternator when it is not charging. The engine MUST be running. There will be 0 volts on both terminals if the engine is not rotating. One terminal must have full battery voltage. The other one must have less but not 0 volts. 0 volts indicates worn brushes. The same voltage on both terminals indicates a break in the circuit somewhere further down the line. That could be an open regulator circuit but suspect a corroded pin in an electrical connector as much more likely.

Caradiodoc
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Sunday, November 14th, 2010 AT 2:33 AM

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