Battery Light is on

ShawnSC1

Registered User
My battery light came on today. So I then tested the battery, and it was ok. The I tested the alt. and it was fine. It was charging at 14.1 volts and the amps were at 79.0. Is there something eles I should check. If not then does that mean my alt. is on its way out. The light stays on all the time while running.
 
did you check a chart to see if 79 amps is an acceptable peak amp rating for our alt. Check all the cables as well.
 
Try calling Autozone and find out what amp the ALT is supposed to be and then ask them to check the chart to see what the acctp peak amp rating is.
 
I have similar problem

I don't want to steal your post here but I was driving my '95 awhile back and all of a sudden the battery light would come on only above 3000 or so rpm. Tested the battery and it was dead. Stole the alternator off my '91 so I could continue driving my '95 and put in a new battery. So I took the alternator in to a reputable shop and they tested it for an hour and said they could find nothing wrong with it. Put the alternator in my '91 and it did the same thing. I now the battery is good so what could it be? Thanks, Brandon
 
My '90 SC batt light was on and voltage read 14+ Volts while running. Took the alternator to a rebuild shop and had them replace everything possible. Cost $144. Re-installed and the batt light went out.

Mine is a 110 amp alt.
 
Also, don't just visually inspect your cables, pull them off and clean all the connections good, including the the cables going to your solenoid on the fender.
 
Yes thats right the ALT can put out volts but not enough amps to run the system and keep the battery charged. Someone on here said before that they just don't build ALT like they used too, well that is not really true, they just don't build cars like they used to. Back in the old day you had a car with a 4 barrel carb now power anyhting and weak head lights, it maybe needed 25-35 amps to run. But back then it would just get a 60 amp ALT. So you end up with an ALT that doesn't have to work very hard at all in order keep the system charged and thus it has a longer life. Now days, if your car needs a 110 AMP Alt to run the system it gets a 110 AMP ALT. So when you add big stereos and pull more power then you are putting an increased load on it. Then it won't last as long.
 
Don't listen to the dopes at Autozone. If your battery light is on Usually it is a dead or dying alternator, typically the internal regulator fails. This internal regulator has a diagnostic line, this line puts out voltage when the alternator is working correctly.

This line runs to your battery light. The other side of the battery light is connected to the run position of the ignition switch. When the system is up and running correctly you should have voltage at both sides of the light, keeping it off. When the regulator detects a problem with the alternator it takes the diagnostic line low, lighting the lamp.

If you have a volt meter check the voltages at the three pin connector to the alternator.

The yellow and white wire should have bettery voltage on it at all times, if not you probably have a burnt fusable link.

The dark Blue wire, if you have one, is not used, It is there only for assembly line diagnostic purposes.

The Light Green and Yellow wire is the diagnostic line. It should be 0V when the engine is not running, and 12V or higher when the alternator is spinning.

This link may be of interest too. It is from when I had my oddball Alternator failure fresh in my mind.

http://pub29.ezboard.com/fthunderbirdscenthusiastclubfrm3.showMessage?topicID=317.topic
 
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Hey, ***. I am a "Dope at Autozone", don't know what your AUtozone is like but most everyone up here has at least 3-4 people working there that have been mechanics for many years, that way when younger people are unsure about something, they have someone they can ask. What everyone else said on here was also correct, the ALT needs to stay above a minimum number of amps. Bottom line is that the machine shows what the peak amp rating was during the test while it is on the car, and then you check the chart for the accectible peak amp rating for the alt. Based on that and the voltage you can determine if it is good, bad, or weak.
 
1BADSC said:
Hey, ***. I am a "Dope at Autozone"

Well, that explains a lot....

I don't care what the chart says, and I have no faith in most autoparts store bench tests.

And if you want to know what the Autozones around here are like, well basically its a toys R us with a few (very few) car parts run by a staff of clowns fresh out of high school auto shop. They are a great place for lighted shift knobs, matchbox cars, and NOS brand steering wheel covers, but the last place the get decent automotive advise.
 
that's nice, but what I am talking about is not a bench test, it is a 5,000 dollar machine that is taken out to your car and tests the ALT in a real world test while your car is running, in order to see what is really going on, it will even tell you if there is a problem with the wiring itself.
 
Name

What is the machine's name? that sounds like some pretty sophisticated equipment, it must be used so that those "Dopes at Autozone" don't need to learn how to use a multimeter and appliy some of those high school shop skills. Oh and Scott, no offence, there are exceptions to every rule.

Dave
 
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sure, we could use an ohm meter if we could stand outside for 10-20 min with every customer that needs to have an ALT and BATT check, but that would be a waste of time, and the BEAR Tester works wonderfuly, As long as the person using it knows what the different readings are. It can also measure the cranking amps of the starting system, and takes into consideration the current outside temperature and the effect that it has on the components as well.
 
Look, We don't need to get into a discussion on how expensive the wonderful test tools at Autozone cost. I know you don't want to stand outside for 20 minutes (It really shouldn't take that long anyway if you know what you are doing) You want to sell parts.

This guys came here looking for help diagnosing his car. Your advise was to tell him to go somewhere else. If you don't want to try and help this guy, keep quiet.

I will tell you that this BEAR thing is not any type of be all end all test equiptment. I had some moron at a Murrays try and diagnose my car with one when I trie dto return a bad alternator they sold me. He fooled around for 20 minutes, insisted my car was screwed up and the alternator was fine. The fact of the matter was the alternator they had sold me was defective, I proved that to him by demonstrating that the car functioned perfectly after replacing the alternator with an OEM part. He gave me all the same arguments about how expensive the tool was, and his training on the tool. Don't take this Machine's results as the last word.

Which brings me to the next point. If the guy in the original post is still reading I would advise getting your new alternator from a Ford dealer rather than one of the chain type parts stores, in my experience the price difference was minimal. They typically get their parts from questionable rebuilders who don't replace anymore than a few parts, usually not the regulator, (unless it is a solid failure), which is the common failure. Also FWIW I say a few, supposedly working, SC alternators on e-bay last night for less than $10.
 
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