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Old 07-24-2011, 11:38 AM   #1
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Default Bad exciter signal to alternator/voltage regulator. 1995 Park Avenue

I've had a charging problem for a long time. When the car is cold, driving in the winter, the alternator works fine, but as it warms up, the alternator charges only intermittently, then stops charging, the headlights go dim, and the battery eventually goes dead. Most of the time in the summer, the alternator doesn't do anything, and the battery goes dead pretty soon.

Here is my understanding of the system design: The alternator gets an input on the terminal L of its voltage regulator. When terminal L gets positive battery voltage, the alternator can charge the battery and supply power to the accessories as needed. When the voltage at L is low, the alternator is turned off, and no power is supplied even if the system voltage is low. Terminal L is connected to an output C260 from the PCM (computer). The input to L is called the exciter wire for the voltage regulator.

We found two problems at Terminal L: a bad connector at the voltage regulator and a flaky signal from the computer. So the alternator was not being turned on by the computer. Please say whether you think our fix was a good one.

We bought a new connector to replace the bad one, and we cut the wire between the PCM and Terminal L. We got into the fuse box beneath the glove compartment and found a fuse for the fuel pump. We soldered one end of a jumper wire to that fuse, ran the jumper wire into the engine compartment, and soldered the other end to the replacement connector for Terminal L and plugged the connector into the alternator/VR.

So now L gets positive voltage when the ignition is on, and the alternator should put out power whenever the engine is running. However there is a substantial drain when the ignition is on and the engine is not running: I measured over 1 amp current through the jumper that way.

The system voltage is good and steady when we run the engine, but I am not sure whether there may be some other bad effect from our fix.

Please advise.
1995 Buick Park Avenue Ultra
CS144 alternator
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alternator exciter, exciter wire, terminal l, voltage regulator exciter

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