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Got voltmeter? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 23 Aug 2006 05:36:22
In Reply to: slowly weakening electrical problem, jake  [Profile/Gallery]
, Tue, 22 Aug 2006 17:11:35
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Let the car cool off. It doesn't have to be dead cold, but don't do this right after a long drive on a hot day.
Put a voltmeter on the battery posts when the engine is running at idle. Have all the accessories off - lights, fan, A/C, radio, the works turned off. The voltage should be above 13.0 volts (13.1 or so OK). Turn on the headlights and blower fan. The voltage should drop, but not more than about 0.5 volts or so - no lower than 12.9 or so.
Do the same measurements - with and without load, on a few other spots. Measure from the negative battery post to the negative battery cable clamp. Measure from the neg post to the chassis ground. Measure between the alternator body and chassis ground. Measure from the positive post to the positive cable clamp. Measure from the positive battery post to the post on the back of the alternator. In all of these tests, expect to see voltages LESS THAN 0.05 volts (50 millivolts), even under load.
If the battery voltage is low (say in the high to mid 12's or so) AND the ground checks are all OK, the voltage regulator is probably tired. I'd replace that before tackling the alternator itself, as it usually isn't the alternator.
If the battery voltage is low and ANY of the grounding type checks are high (more than about 0.05 volts), find and fix those problems. It might be a bad connection from battery post to clamp; a bad battery cable (not uncommon), or a bad alternator ground (very common).
If everything checks out and you are still having issues, I'd have to recommend digging into the wiring, to check the common power bus for those devices. It may be corrosion in the fusebox. But check the power source (alternator, battery, wiring) first.
posted by 192.249....
, Tue, 22 Aug 2006 17:11:35, Wed, 23 Aug 2006 05:36:22 <-- Viewing This Message
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