Why isn't my charge system working?

Tiny
BACKYARD MECHANIC
  • MEMBER
  • 1989 LINCOLN TOWN CAR
  • 117,000 MILES
The "Charge System" warning message appeared on the message center. I assumed this was the alternator failing. I connected a battery charger and found the battery to be holding charge and 12.6 volts at rest. I bought an alternator from my local pep boys and installed. No difference - message still appeared and Batt not charging. Didn't realize but the 100 amp alternator has an external voltage regulator. Found one at my local Auto Zone replaced it. Still nothing - message and no battery charge continues. What do I do next?
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Saturday, November 5th, 2011 AT 5:06 PM

8 Replies

Tiny
CARADIODOC
  • EXPERT
Look for a blown blue 15 amp fuse. Next, measure the voltages on all of the wires while the engine is running, then holler back with those numbers.
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Saturday, November 5th, 2011 AT 5:47 PM
Tiny
BACKYARD MECHANIC
  • MEMBER
12.1at batt and batt connection at alternator, at plug in connector the front wire (field possibly) 0.1 volts, rear wire (stator?) 0 volts, at regulator: I connection 0.9 volts, A connection 12.1 volts, S connection 0 volts, F connection 0.1 volts. No blown fuses
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Saturday, November 5th, 2011 AT 7:00 PM
Tiny
CARADIODOC
  • EXPERT
Do you have wire colors to go with the voltages?

12.1 at the battery wire is correct. If there's 0 volts at the stator (white or white / black), that means there's no output. That tells the regulator to turn on the battery warning light. "A" is system voltage sensing and should be 12.1 volts. The field should be higher. The higher the voltage, the higher the current flow through the brushes and field winding. The higher the current flow, the bigger electromagnet it makes. The bigger the magnet, the more output current you'll get. With 0 volts on the field, there won't be any output generated.

When you measure these voltages, measure at the generator and at the regulator to be sure you have the same voltage on each end of each wire. If one has different voltages, look for a corroded wire or a loose terminal in a connector.
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Saturday, November 5th, 2011 AT 8:58 PM
Tiny
CARADIODOC
  • EXPERT
Be sure the voltage regulator is bolted solidly to the body too. It needs a good ground to work.
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Saturday, November 5th, 2011 AT 8:59 PM
Tiny
BACKYARD MECHANIC
  • MEMBER
What does the I terminal (green with red stripe) of the regulator do? With ignition switch in run and nearby connector disconnected, the green w/red stripe wire has 11.7 volts (battery at 12.1). Reconnect the regulator and it drops to zero volts! Also it was red with blue stripe that has 0.1 volts while car runs and white with blk that is zero volts.
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Monday, November 7th, 2011 AT 8:35 PM
Tiny
CARADIODOC
  • EXPERT
Sorry to leave you hanging. Have you solved the problem yet? The green / red wire provides the turn-on signal for the voltage regulator. With the plug disconnected you'll be reading the 12 volts that comes through the ignition switch and dash warning light, (or a resistor that replaces that light on some cars). It went to near 0 volts when plugged in because the regulator was grounding that wire to turn on the warning light. When the system is working about 6 volts appears on the white / black wire to tell the regulator to turn the warning light off. THAT'S when you should again find full battery voltage on the green / red wire.

Look for a yellow wire in the connector. It should have full battery voltage all the time. If it doesn't, a fuse or fuse link wire is blown.

That connector is part of the voltage regulator. It's held on with four small bolts in a rectangular pattern. If you can see back there, you'll find two additional bolts. One might be covered with a plastic cap. The other one has printing stamped next to it that says "Ground here to test". Use a piece of wire to ground that bolt while the engine is running. If the headlights get brighter and the system voltage goes up, the regulator is defective and can be replaced separately. If there's no change in system voltage, further tests will determine the cause but worn brushes are the most common thing to find. They come as part of a new voltage regulator. I can walk you through the testing procedure. You'll need an ohm meter or test light.
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Monday, November 21st, 2011 AT 10:24 AM
Tiny
BACKYARD MECHANIC
  • MEMBER
Hey thanks for getting back, the problem continues. I work retail, getting time away from my store is hard this time of the year. The regulator is external of the alternator, mounted on the wheel well. I don't see anything that says ground to test. I will check yellow wire this afternoon. Thanks again!
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Monday, November 21st, 2011 AT 11:45 AM
Tiny
CARADIODOC
  • EXPERT
There's two different generators for your car. I got sidetracked searching for a diagram with the correct wire colors on the external regulator version. For now, jumping between the "I" and "F" terminals on the regulator will bypass it and "full-field" the generator. Those should be the first and fourth terminals. That will make it charge wide open if the regulator is at fault. Don't raise engine speed and definitely don't disconnect the battery when doing the full-field test. Either of those things will allow system voltage to rise to dangerous levels if the generator is working.

If bypassing the regulator makes the generator work, you'll see the head lights get noticeably brighter, or, if you're monitoring battery voltage with a digital voltmeter, you'll see the voltage go up to around 14 to 16 volts at idle. That will prove everything other than the regulator is working.

If bypassing the regulator causes no change in output voltage, the problem is in the generator or wiring. I can walk you through that diagnosis once I find a diagram.
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Monday, November 21st, 2011 AT 8:55 PM

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