What causes the battery light to be on?

[jcode68]

I have a 2000 GT with 105k miles on it, all original, no aftermarket parts. While driving home the other night, the battery light on the dash came on. Everything was fine for a while, but eventually the lughts went dim and the voltage guage dropped all the way down. The car eventually died and I had to have it towed home. I thought initially it was the alternator, so I took it out and had Advanced Auto Parts test it. They said it tested fine and had good output. The battery is original, so I suspected it needed to be replaced anyway. Had Advanced test the battery - it failed. I put in a new battery and replaced the connection on the + battery cable since it was badly corroded and essentialy snapped when I removed it. The new connection I put on screws on to the OEM cable and seems to have a nice solid connection. I checked all other connections and put everything back together. Started the car and everything seemed fine and shut it down after running for about 2 minutes. Went back a couple of hours later and started the car and the battery light on the dash is on again. A new alternator was $200, so I don't want to just guess that this needs to be replaced. What does the battery light acutally indicate? I searched this forum for threads, but could not find anything relevant. Thanks in advance for responses.

 

[myponyrocks]

could be your altenator going bad

 

[jcode68]

Thanks for the response. I was thinking that as well, but wanted to have more info before getting a new one since they are pretty expensive. What confuses me is the parts store tested my alternator and said it tested fine?? What causes the battery light to come on?

 

[flexiclese]

When the battery light comes on it means your charging system is not putting out a sufficient charge. Before running out and buying a new battery and alternator check all your connections to make they're clean and connected solidly/not loose, make sure there are no breaks in the the wiring that might be shorting out. Be sure to check the ground connections, to the body, engine and trans.

 

[jcode68]

When the battery light comes on it means your charging system is not putting out a sufficient charge. Before running out and buying a new battery and alternator check all your connections to make they're clean and connected solidly/not loose, make sure there are no breaks in the the wiring that might be shorting out. Be sure to check the ground connections, to the body, engine and trans.

Thanks for the response. I had both the alternator and battery tested - alternator passed, battery failed, so I replaced the battery. I replaced the + battery cable connection since it was coroded and broke when I tried to remove it from the batt post. I checked all the connections and all others seem to be fine. Is it possible the alternator could be intermitently failing? Last week over the course of a couple of days driving the car, the battery light would come on for a bit and then go off for a while. Each time I would check the voltage guage and it never moved. What is the procedure to test the alternator while it's in the car? I have a volt meter, but admit I'm not very good with it.

 

[masicinap]

I got the same problem except my lights dont dim and the car doesn't shutdown. I just replaced my battery less than a year ago. i'm curious as to what it could be also.

 

[flexiclese]

Thanks for the response. I had both the alternator and battery tested - alternator passed, battery failed, so I replaced the battery. I replaced the + battery cable connection since it was coroded and broke when I tried to remove it from the batt post. I checked all the connections and all others seem to be fine. Is it possible the alternator could be intermitently failing? Last week over the course of a couple of days driving the car, the battery light would come on for a bit and then go off for a while. Each time I would check the voltage guage and it never moved. What is the procedure to test the alternator while it's in the car? I have a volt meter, but admit I'm not very good with it.

This sounds like a loose connection or intermittent short. trace all wiring goin to from the alt. and battery to make sure it is all in good shape again (no holes or cracks in wiring), make sure that everything is attached tightly and clean, not corroded. Then do the same with the grounds.

 

[myponyrocks]

Thanks for the response. I had both the alternator and battery tested - alternator passed, battery failed, so I replaced the battery. I replaced the + battery cable connection since it was coroded and broke when I tried to remove it from the batt post. I checked all the connections and all others seem to be fine. Is it possible the alternator could be intermitently failing? Last week over the course of a couple of days driving the car, the battery light would come on for a bit and then go off for a while. Each time I would check the voltage guage and it never moved. What is the procedure to test the alternator while it's in the car? I have a volt meter, but admit I'm not very good with it.

Disconnect the battery for about 8 hours or so, connect everything up in the morning about 15 min before you normally go to work or whatever. Do the normal reset procedures... maybe the light is just still on?

It still seems like Alt. to me, but if they tested it good that doesn't make sense, plus you're saying you replaced the cables allready, so I'm stumped.

 

[jcode68]

I'm stumped too - I checked all the connections and cleaned any corrosion, so all connections should be solid. When I first started the car after replacing the battery everything was fine - no light. I shut it down and went back a couple of hours later and started it and the light was back on. Maybe I will try wiggling some wires while it's running and the light is on to see if I can locate a bad wire as part of the problem. I'm wondering if it's a problem iunternal to the alternator which is intermitent. I don't have a problem repolacing the alternator since it's the original with 105k miles on it, I would expect to as part of maintenance. But if it doesn't solve the problem I will be pissed since they are $200 at the low end for an aftermarket. Any last minute words of advice from any of the Ford mechanics who frequent this forum (other than take it to a Ford mechanic ;-)?

 

[myponyrocks]

you don't happen to have an aftermarket stereo do you?

 

[jcode68]

you don't happen to have an aftermarket stereo do you?

Nope, factory Mach 460.

 

[XtorT'r]

How is the serp belt doing? And do our cars have seperate regulators or is that built into the alternator?

 

[BlackGT4.6]

I have seen many alternators come in our shop and test fine until they warm up. It is a good possiblity that your alternator is bad and testing good.

 

[jcode68]

I have seen many alternators come in our shop and test fine until they warm up. It is a good possiblity that your alternator is bad and testing good.

This is good to know. I would assume an alternator failure after 105k miles would not be surprising. This may explain why the problem is intermittent. Regarding the serpentine belot - I replaced it approx 10k miles ago and it is in good condition.

 

[Dan_Soprano]

sounds like a bad ground to me.....replace the ground wire on the battery.