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Discussion Starter #1
My battery light came on, and has been on, all day today while I have been driving. I know this usually means bad alternator, weak bateery, or loose wires somewhere.

So I bring out the DMM and do some testing. After I first noticed the battery light come on, I have to drive about 5 miles to home. Figure the battery (Optima Red Top, about 8 months old) would show a decent amount of voltage loss if the alternator was bad. Put the DMM on it, and about 13v..... weird.

Start the car up, test the voltage on the battery again..... 14.5v.... double weird. The alternator is running fine, putting out full power. I turned on the radio, headlights, AC, etc, and hardly ANY voltage drop at all.

Check all wires, power ground, etc, and everything is fine. I have now driven for about 60 minutes or so with the battery light on. When I turn the car off, battery still reads about 13v.

So WHY THE HECK IS THE BATTERY LIGHT ON?

also, I have turned the car off and restarted multiple times, and the light is on everytime. The car has no problem whatsoever turning over, starts like usual. I'm starting to think there might be a problem with the bulb for the battery light!
 

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Maybe the voltage regulator went out on the alternator. Sending that light on for a MAX voltag. Just a long shot, because a stock alternator or even High output wont put out 14.5. Thats pretty damn high.. I HAVE a High output, and I MIGHT get that 14.5v. Especially if there is no voltage drop when you turn the AC and or lights on. just my .02 worth a shot, see if you can pull a code, stating too high a voltage or something of the sort.
 

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Discussion Starter #3
Forgot to mention, mine is a high output alternator....

I don't understand the begining part of your post... what exactly do you want me to try?

If I turn things on, the voltage DOES drop, but not by a huge amount.
 

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Ok, Well I DO have a High output also. What i was trying to get at, is maybe the voltage regulator is going or IS bad, causing a high voltage issue, which in turn might turn that light on. That is just a guess, if there is no other issues. How long has the altnernator been in the car?
 

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Discussion Starter #5
about six or seven months, I'd say. The voltage isn't anything weird. It has always been around 14.4-14.5v since day one.
 

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Discussion Starter #6
UPDATE

Today the car started doing something weird again. The battery light has been on since I posted about it, but now a new problem. SOMETIMES, not every time, when I come to a complete stop and put it in first gear, the car just dies. It doesn't shake like when you take your foot off the clutch w/o giving it gas, it just gently dies. Any ideas?
 

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I have heard of that problem before. I thought there was a TSB on it. Something about stalling during operation. My friend has an ATX 01 wagon which dies sometimes too. It only has been happening when it's hot/humid out like it has been lately. I think a reflash fixes it, but I can't remember the reason, might wanna PM WD40 and ask him about it.
 

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Discussion Starter #8
took it to Advanced. No codes were being put out. Check battery and alternator, everything was fine. Belts were all fine. He saidthe only thing he could think of would be a glitch with the attery light itself. I'm still taking it to the shop tomorrow.

Oh, and it hasn't stalled since earlier. Humidity has gone down, wonder if that is what caused it?
 

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My 02 svt has been having the same problems. Whenever i get into the high rpms on the highway the battery light comes on. Last night i got onto the highway, there was a electrical burn smell coming from my vents. The battery light came on and stayed on for 5 minutes. Then it went off. Everything
checks out fine but im going to replace it just in case.
 

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Just to put the record straight- a 'High Output Alternator' does NOT output more volts. It WILL output more current, but the voltage is always between 13.8 to 14.4 volts.

You might want to check the pigtail wiring on the back of the alternator. This is a known weak point on the Focus and could cause your problem.
 

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Thanks for the reply-just poking around the alternator looks like trouble-is it easier to get the hands in there than it appears at first blush, or do I first need to remove everything north of the dashboard to get at it?
 

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Never done it myself I'm afraid- so can't advise. Plenty of others have, so a search on this Forum should give you the answer.
 

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On more than just on forum, I got the distinct impression that the Ford Focus had some sort of mystery surrounding my Battery light symptom. At least four instances were cited where the post indicated both battery and alternator replacement did not resolve their battery light issues. $120 for a battery, $600-800 I read were typical costs for alternator replacements, all to no avail. From this, I concluded that there was some other potential cause for my problem.

I ended up buying a new battery, based on the results of a test by a local shop. Not the answer. I decided to put the old battery back in and drive the car till something fell out of it. Then, I would be certain of the defective component.

My alternator toasted on Saturday night. As I might expect, once the alt finally gave up the ghost, the appropriate computer shut off all non-essential electricals, providing all available power to the engine (and, I supposed fuel pump) until the battery was too exhausted. It got me as far as I needed to go.

In NJ, one of the few service agents open on Sunday was Pep Boys. They secured an alternator from NAPA and installed it in a couple hours for $472. No mystery, no rocket science.

Seems like my ST and I are back in Focus.

Now, onto the reverse light switch.

(The hidden message here-don't overcomplicate this. The way my alternator failed-lots of strange electrical issues. The grand finale-all electricals shut down until the battery was dead.)

I'd replace the alternator. If you're not confident doing it yourself-I wouldn't hesitate to take it to Pep Boys (as silly as that sounds). From what I've read-they gave me a solid price.
 

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"The hidden message here-don't overcomplicate this"
Hindsight is a wonderful thing. With all problems it is difficult to arrive at the final solution without going through all the possibilities based on the information to hand. In my experience, the only time a battery light has come on was when the alternator failed. You had a fairly recent alternator but it was proven to be faulty. We could have said- change the alternator- and the problem could have been the wiring. Glad you have solved your problem though.
 

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Now, onto the reverse light switch.

I'd replace the alternator. If you're not confident doing it yourself-I wouldn't hesitate to take it to Pep Boys (as silly as that sounds). From what I've read-they gave me a solid price.

I have a contributed to a thread on this, its quite simple and likely the switch.

I had identical symptoms to your alternator, when a load was applied it would drop just below 13v. I changed the alternator myself, it took 2h out and about 30min back in. doing it again, i could probably have it out in about 30. it is a bit of work but only nut and bolt work. Its a good excuse to change the belt and i replaced the tension idler at the same time as the bearing was trashed.
 

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I had this problem. I could not figure it out. My alternator went bad so I replaced it. After replacing the alternator the battery light came on (was not on before). I then replaced the belt and checked voltage under all different loads with lights and a/c on. Everything worked perfect. Even had autozone test it. I decided to pull the bulb out of the dash. That was my simple solution to worrying about it anymore.
 

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The battery light in my car came on while driving. After I turned the car off I noticed that the battery light came on each time about 15 seconds after starting the engine. I checked the charging voltage and amperage with a digital mulitimeter- charging system was working but rather weak. The next day I fully charged the battery and took the car out for a drive...the battery light was on the entire time and the car completely died with a dead battery about 30-40 minutes after driving. All this while my multimeter was showing alternator output (however low and weak).

I decided to upgrade and ordered a new Bosch hi-output replacement (220 amp) for $249.00 shipped from an eBay seller since I live in a hot climate, run the air conditioner, and also tend to run a power inverter and other electrical accessories inside the car. I installed the alternator myself- took me about 3hrs.

Battery light no longer comes on. Charging voltage is a solid 14.2-14.4 volts off-idle. I didn't check the charging amperage because it would probably fry my multimeter.

But now I have a new "problem". This new Bosch hi-output alternator seems to have to spin at a higher RPM before it kicks in and actually charges. My car idles at about 700RPM and I am getting less than 12.5v at the battery. If I increase engine RPM to 900 then charging voltage immediately jumps to a solid 14.2-14.4v. The Bosch alt has the same diameter pulley as the OEM alt I removed, so alternator shaft speed is exactly the same.

I mostly drive my car in the lower RPM ranges and also do a lot of relatively shorter distances in city (ie. stop and go driving), so this poses a problem - my battery now is usually discharging considering the way I drive, unless I hit the open road or something (which I don't do too often).

I never had this low rpm charging issue with the stock alternator :(
 

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Posted via FF MobileSeems like the current problem is a lower than normal Idle RPM. Mine Idles at about 900 when warm, and readjusts to that when A/C is engaged (pops higher then settles down) so that seems like the normal speed for idle. If the IAC seems to be responding normally you may have a vacuum leak or other cause for low idle.... Others may know your normal idle, I can`t see your model info on Mobile, just guessing that all models have similar std. Idle RPM....
 
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