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Old 07-23-2010, 02:44 PM   #1
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Alternator output fluctuates (sometimes)

I've seen many posts regarding alternator output but none quite llike this.
The problem starts with what seems to be a loss of power. THen we will experience flickering of lights. Both head lights and dash lights.
I have checked belt tension on the alternator and it seems to be fine (new belt) and the tensioner is good. Put a meter on the battery and it registers 12.74 volts. Checked alternator output at the battery and I get fluctuations of 13.9, 12.83,14.10 volts and so on, up and down. Then the unit settled down at a fluctuating 14.2 volts.
Next day I ran the same test and the alternator settled in at 114.5/14.6 volts. No fluctuations this time. Put a load on the alt. (headlights and blower) and saw a voltage decrease to 13.8/13.7.
I would think this indicative of a faulty regulator but not real sure. I thought I had this fixed as I had disconnected the leads to the alternator and cleaned everything up and it was good for a day or two.
Any ideas?


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Old 07-23-2010, 04:03 PM   #2
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Solid state regulators either work- or they don't. If you have a Zetec, the most likely cause of your woes is the wiring to the alternator. It is a known troublespot on the Focus. Do a search on this Forum and you will find a wealth of info on checking and fixing the issue. Good luck.
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Old 07-23-2010, 04:59 PM   #3
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I had similar symptoms with mine, kinda. It would produce full voltage output with no load. when the electrical system was loaded the voltage output would drop below 13v.

much of the fluctuation is noise in the meter or resistance in the probe contact. some fluctuation is always present when taking such measurement. all voltage tests should be performed with a high idle, 1500-2000rpm.

what symptoms were you having to prompt such investigation? there is the famous alternator plug problem, check that out first... as replacing the alternator on the zetec is a _itch.
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Old 07-23-2010, 05:39 PM   #4
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Arlenn,

First indicator was the infamous fading lights and hesitation as if the belt is slipping. I think I will buy the alt. pigtail and see where that leads. I had at one time pulled the alt. connector and cleaned all contacts and that seemed to work for about a week, maybe less. Seems like a change of alternator would be easiest from the underside.
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Old 07-24-2010, 08:18 AM   #5
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Also, be sure all battery & ground connections are clean & tight. I have seen a couple that were loose causing this problems.
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Old 07-28-2010, 02:48 PM   #6
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So I replaced the alternator pigtail. Cost $37.00 at the ford dealership. Inspected the leads at the harness and found the wire to be in great shape. Cut the old plug from the harness and soldered and shrink tubed the new connections. Plugged the new connector in and all seems well. That's what I thought last time so only time will tell. No voltage fluctuations this time so that is promising.
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Old 07-28-2010, 06:56 PM   #7
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See that large wire that is crimped to the positive battery clamp. What if that crimped connection was intermittent?
That large wire goes to the alternator and starter
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