Battery light on, but still charging

[oharris]

My battery light came on while I was driving home from work. It does this occasionally, but it always goes out after a while. The amp gauge still shows a normal charge and the lights don't dim or anything so it's apparently still charging. What could be causing this? 97 Mountaineer

 

[FIND]

I would guess that the post on your alternator is bad. Try taking the lead off, I'd be willing to bet the post will feel loose.

If not, you are going to have to find a better way to monitor voltage. You could also take your truck to somewhere like Walmart and ask them to test your battery, which they will do for free. When they test your battery, they will also do a charging system test, so you can see if there are any obvious problems that way.

 

[1996BLKBauer]

Same what FIND said, seems like a loose connection to either the post, or the plug. If the light goes on, try and get a volt meter, and see what the reading is at the battery. It should say 14.6V or close to that.

 

[oharris]

It did it again this morning on the way into work. While it was on I tried turning on the headlights and turning the heater blower up to high. The voltmeter on the dash (I said amp gauge in my first post, but it is a voltmeter) dipped right as I turned it on but came right back up. That tells me it's still charging. The battery has never discharged either, it always starts right up, even on cold mornings.

I'll take a look at the alternator post and get it tested at Autozone or something as you have suggested, but I would think if it were something like that then it wouldn't charge.

 

[albi1cnobi1]

I don't think it's charging. It looks like you just happen to have a good battery. If you get it checked and you have 14+v at the battery then the alt may still have a problem, because it provides a ground when it's not charging to turn on the battery light. The other option is a wiring problem between the alt and the light. Here's the wiring diagram. Maybe it will help you troubleshoot your problem.

 

[koda2000]

the voltage regulator turns off the BATT light when the alternator is putting out sufficient voltage. if the light comes on intermittently you either have a bad connection or (more likely) your alternator/voltage regulator is on the way out. s/b 14.6 volts tested at the battery engine running.

 

[oharris]

I think it is charging and here's why I think so. I also have a 2000 Explorer, and that one has an issue where the belt slips right after a cold startup, especially if you have left the heater blower on high or turned on the headlights. It stops squealing after a minute or so and everything returns to normal. While it's slipping, the voltmeter is noticibly lower and the lights are noticibly dimmer. (ironically, the battery light never turns on.) That's what a no charge or low charge should look like.

I also did a lot of searching here, and every case I could find, the voltmeter was also low in addition to the light being on. Most also had dead batteries, stalling engines and other things you would expect of a bad charging system. All symptoms I don't have.

Then I found this thread: http://www.explorerforum.com/forums/showthread.php?t=377576 His symptoms seem to match mine exactly, so I'm going to try his solution. I'll let you all know what I find out.

 

[koda2000]

the "volt meter" on your dash isn't really a volt meter. don't just think it's ok. get it checked. it's free at most auto parts stores

 

[oharris]

the "volt meter" on your dash isn't really a volt meter. don't just think it's ok. get it checked. it's free at most auto parts stores

What is it then? Certainly doesn't measure amps.

 

[albi1cnobi1]

It's not a "true" volt meter. Meaning its only a gauge, its not very accurate at all. A real volt meter's circuitry is much different and measures differently. I think thats where koda2000 was going.

 

[budwich]

As suggested both in this thread and the other referred to one, check your connections to ensure they are tight AND clean. Further, I do believe the "voltmeter" display passes thru a "slop circuit" to prevent the meter from jumping around all over the place... so it really isn't an "instantaneous" meter... thus if you have a "loose connection"... that "fault" might readily set the charger light BUT not reflect in the meter. It will likely "bite" you in the long run if you don't find the root cause.

 

[1996BLKBauer]

They make the meters on the dash dumb, it is slower, so people don't think the truck is broken when it moves like crazy with engine, and load differences, and it is designed to stay in the center, which most people think is good. If it was truly accurate, Ford would have everybody come in complaining about it.

 

[oharris]

I finally got a chance to look at this. I did a little experiment first in which I checked the in dash meter with the key on, engine off and headlights on. Then I started it to see if I could see a difference. Sure enough I can easily see the difference between what should be about 12V and about 14V. So I believe the meter is accurate enough to tell if the alternator is charging or not.

I looked at alternator wiring and it's a bit different than the diagram that albi1cnobi1. There are only three connections. The heavy charge wire and two wires in the plug that goes into the regulator. albi1cnobi1's diagram shows a short jumper wire that goes between the regulator and the stator. I'm assuming that connection is made internally in my application (The diagram is labeled "4.0L" and I have a 5.0L.) There is a wire that matches the color of the wire that is shown going to the light. Everything looked fine but I then discovered that I was out of electrical cleaner, so I'll have to get some and see if I can clean it up.

Naturally the light hasn't turned on since Tuesday. Don't you just love intermittent problems?

 

[budwich]

BUT there are "things" other than numbers involved potentially. The dash meter may not actually read a signal that has an issue with "dc signal" this missing some rectification... ie. loss of internal rectifier.

 

[oharris]

BUT there are "things" other than numbers involved potentially. The dash meter may not actually read a signal that has an issue with "dc signal" this missing some rectification... ie. loss of internal rectifier.

While that is true, I would expect other problems such as fried batteries and other electronic dodads. I don't think the light would indicate that anyway would it?

Incidentally I did put my multi-meter on it and it showed 16V key off and 18V running. I thought I had found my problem, and you guys were right about that meter being inaccurate. Then I wondered why I don't have lights burning out left and right. So I checked two other vehicles with that meter and they both read 16V key off. So either all three are over charging or my meter is bad. I'm going with the latter.

 

[albi1cnobi1]

I looked at alternator wiring and it's a bit different than the diagram that albi1cnobi1. There are only three connections. The heavy charge wire and two wires in the plug that goes into the regulator. albi1cnobi1's diagram shows a short jumper wire that goes between the regulator and the stator. I'm assuming that connection is made internally in my application (The diagram is labeled "4.0L" and I have a 5.0L.) There is a wire that matches the color of the wire that is shown going to the light. Everything looked fine but I then discovered that I was out of electrical cleaner, so I'll have to get some and see if I can clean it up.

Naturally the light hasn't turned on since Tuesday. Don't you just love intermittent problems?

That connection is made internally, on both the 4.0 and the 5.0

 

[budwich]

I didn't you that the rectifier was "gone". If you have a poor / intermittent connection / joint in the bridge, it might be enough to turn on the light and still not have an "issue" with the meter... your hand meter included as the DC scale won't necessarily indicate a problem with a "lost lobe" or two. You won't be frying any batteries but you won't necessarily be getting full charging either... eventually. Anyways, hopefully time won't tell ...