Alt light on while running?

[mattchee]

Hey all - I'm new to this forum (well, I've lurked), and I am admittedly a bit of a novice when it comes to working on/troubleshooting cars. But I'm and eager learner! ANYHOW, here's my question that hopefully someone can shed some light onto:

I have a 65 with a 200cid I6, which is a weekend driver (I wish it was daily, but I have a 40 mile commute, and I'm still working out the bugs). A fixer upper to be sure. Anyhow, I think this may apply to any car though.

Last weekend, when I took the car out for a spin, the ALT light stayed on while it was running. I ran my one errand and drove it straight home (about 2 miles away). While running, the alternator was spinning, everything LOOKED fine. After I turned off the car, I pushed on the alternator fan blade, and it spun independently of the fan/engine so I assumed the fan belt was possibly too loose to run the alternator properly. I started up the car again, just to see if it would, and it did so without any problems. Unfortunately, I didn't have any time to do anything about it until this morning.

This morning (one week later) I tightened up the fan belt and and went to start the car. Click click click. Dead battery. SO, I gave it a jump from my other car and it started right up. The ALT light was still on while it was running though. I let it run for about 5 minutes while inspected the engine to make sure that the alternator was spinning, etc. Since the ALT light was on, I assumed it wasn't charging so I didn't bother keeping the engine running. I turned it off. Turned it back on again (I dunno, I was curious), and it started right up. Turned it off, pushed on the alternator fan to see if it still slipped, and it did not. Attempted to start again - click click. dead battery.

My FIRST thought would be that the alternator is bad, but I have this nagging feeling that the battery is bad. I have the feeling about the battery because it seems to have lost its charge over the week while the car was not operating (how would have drained?) And if the alternator was not charging, how did the car remain running for those five minutes with a dead battery?

So I guess my question would be could a bad battery even cause the ALT light to come on, or does it only come on as a result of a charging issue?

And, what do y'all think about my situation?

I don't have the equipment to do a proper electrical test, unfortunately, so I was attempting a little process of elimination, but at this point, its going to start getting a little costly.

Any thoughts on this would be greatly appreciated. Sorry for the long winded description of my problem, but I the more info I give... the better!

Thanks!

 

[hhead]

First, I would fully charge your battery with a charger. I don't think a few minutes of running, after tightening your belt, is enough to charge your battery.
Your car will run w/ a bad alternator. I've had my car running down on 10v or so, before on just the weak battery.
After the full charge your car should fire up easily. You could take the alt in to a parts store for a free test. The charging system is easy on our cars. Alt and voltage regulator. I'd say the odds are for a rebuilt alternator.
They have rebuild kits for the alt. Easy do it yourself. Kit includes new brushes, which are the main culprit in a high mileage alt. I don't think they include the bearing on the back of the case. But that would most likely be squealing if it was bad. They even have upgrade kits for more amps. The kit I've used before was made by 'Quick Start'.
Here's a link to some kits, Ford Alternator upgrade & repair kits, Quick Start Rebuild Kits
Your battery draining could be alt related. As the the diodes in the alt could go bad, and allow drain to ground.
I've never seen a bad battery cause the alt light to go on. But that's just my experience.

 

[PoppyMod]

Hey all - I'm new to this forum (well, I've lurked), and I am admittedly a bit of a novice when it comes to working on/troubleshooting cars. But I'm and eager learner! ANYHOW, here's my question that hopefully someone can shed some light onto:

I have a 65 with a 200cid I6, which is a weekend driver (I wish it was daily, but I have a 40 mile commute, and I'm still working out the bugs). A fixer upper to be sure. Anyhow, I think this may apply to any car though.

Last weekend, when I took the car out for a spin, the ALT light stayed on while it was running. I ran my one errand and drove it straight home (about 2 miles away). While running, the alternator was spinning, everything LOOKED fine. After I turned off the car, I pushed on the alternator fan blade, and it spun independently of the fan/engine so I assumed the fan belt was possibly too loose to run the alternator properly. I started up the car again, just to see if it would, and it did so without any problems. Unfortunately, I didn't have any time to do anything about it until this morning.

This morning (one week later) I tightened up the fan belt and and went to start the car. Click click click. Dead battery. SO, I gave it a jump from my other car and it started right up. The ALT light was still on while it was running though. I let it run for about 5 minutes while inspected the engine to make sure that the alternator was spinning, etc. Since the ALT light was on, I assumed it wasn't charging so I didn't bother keeping the engine running. I turned it off. Turned it back on again (I dunno, I was curious), and it started right up. Turned it off, pushed on the alternator fan to see if it still slipped, and it did not. Attempted to start again - click click. dead battery.

My FIRST thought would be that the alternator is bad, but I have this nagging feeling that the battery is bad. I have the feeling about the battery because it seems to have lost its charge over the week while the car was not operating (how would have drained?) And if the alternator was not charging, how did the car remain running for those five minutes with a dead battery?

So I guess my question would be could a bad battery even cause the ALT light to come on, or does it only come on as a result of a charging issue?

And, what do y'all think about my situation?

I don't have the equipment to do a proper electrical test, unfortunately, so I was attempting a little process of elimination, but at this point, its going to start getting a little costly.

Any thoughts on this would be greatly appreciated. Sorry for the long winded description of my problem, but I the more info I give... the better!

Thanks!

Hi,
First, if you are going to keep this old junk, like the rest of us, buy a shop manual specific to your car. Next, since this is a charging issue, purchase a VOM (volt meter). They are not expensive and will help with future electrical issues. If you can borrow one, charge the battery again, start the engine. Using your VOM, select the DC voltage setting. Place the red lead on the positive terminal and the black lead on the NEG. terminal. If the ALT is not charging, you will get about a
12v reading. A good ALT will read 14 or more volts, indicating more current is going to the battery than is being consumed by the accessories. The good news is most all auto supply stores can check ALTs and starters. My guy feeling is it's bad. As anoth poster has mentioned, they can be repaird at home. However, since you stated you have limited tools, you probably will have to rely on having it tested, then, go from there.
Good Luck!

 

[mattchee]

Thanks for the tips guys! MUCH appreciated. I'm going to start with checking out the alternator.

Definitely keeping "this old junk." Had a 65 w/ I6 when I was in high school (mid 90s), which my dad helped me with at the time - unfortunately it was stolen - father in law found this one for me, runs good, but needs a lot of work, so I'm planning on doing a lot of learning (my dad and I are a good 300 miles apart these days). I'll have to get some pictures up here at some point (though, right now, you kinda gotta be about 100 feet away for it to look good!).

Anyhow, I will keep you posted on what happens with the alternator...

 

[mattchee]

WELL, sorry it took me so long to get back here and update my situation. It was almost a week before I could really do anything anyway.

So, it DID turn out to be the alternator. Didn't feel totally comfortable re-building it, though, so I just bit the bullet and bought a new one. Put that baby in, and it started right up! Didn't even need to jump the battery (which I guess means that it when it was acting dead before, it was really part of the alternator problem, and not a dead/weak battery at all).

Thanks for all the help guys! On to the next thing....

 

[2+2GT]

Hi,
First, if you are going to keep this old junk, like the rest of us, buy a shop manual specific to your car. Next, since this is a charging issue, purchase a VOM (volt meter). They are not expensive and will help with future electrical issues. If you can borrow one, charge the battery again, start the engine. Using your VOM, select the DC voltage setting. Place the red lead on the positive terminal and the black lead on the NEG. terminal. If the ALT is not charging, you will get about a
12v reading. A good ALT will read 14 or more volts, indicating more current is going to the battery than is being consumed by the accessories. The good news is most all auto supply stores can check ALTs and starters. My guy feeling is it's bad. As anoth poster has mentioned, they can be repaird at home. However, since you stated you have limited tools, you probably will have to rely on having it tested, then, go from there.
Good Luck!

What he said, especially get the factory service manual.

WELL, sorry it took me so long to get back here and update my situation. It was almost a week before I could really do anything anyway.

So, it DID turn out to be the alternator. Didn't feel totally comfortable re-building it, though, so I just bit the bullet and bought a new one. Put that baby in, and it started right up! Didn't even need to jump the battery (which I guess means that it when it was acting dead before, it was really part of the alternator problem, and not a dead/weak battery at all).

The car "started right up" because the battery was fully charged. You could take your alternator off and throw it in Lake Michigan, and if the battery is charged, it will still "start right up". Now, if your alternator was bad, and is now good, with ALT light staying off, that's good. As stated above, though, it takes more than a few minutes to get a charge on the battery, more like half an hour, above 1000 rpm.

One note, the hard-core guys around here highly prize the original alternators. The design of the case changed in the 1970's, so the one you have now is probably the wrong style case. Restorers actually pay money for these original cases. It's getting to the point that one of the main suppliers of rebuilt "correct" alternators is so short on 'cores' they are having the cases reproduced.

 

[hhead]

Usually, a soldering iron is the most difficult tool you'll use on rebuilding it. That kit came with instructions. And pics.
Next time give it a try, any problems, ask away.
You'll save $$ and see how easy it is.
Like always, after rebuilding stock. You'll say, "I should have went bigger" lol