i just had alternator and batteries tested they are where there supposed to be but my battery light still stays on its will stay on for miles down the road and go out then i might stay off awhile or it comes back on. i have checked all the visable wires for a short could the light in the dash go bad how do you go about checkin that thnx

 

This happened to me when I got the truck stuck in the mud I was going the replace the alt so I tried to clean the old one first got the water hose and let the water go in the alt got all the mud out let it dry put it back in and the light never came back on. Don't know if you want to try that could mess up the alt.

 

Try getting the alternator tested at a different store. I've had alternators bench test good on a work truck, yet the battery would drain driving the truck and cause a no start. Jump start the truck and drive down the road with no issues except the light, until it came time to get jumped again. Replaced the alternator and no more problems.

 

I once had a belt that was loose enough to not spin the alternator as fast as was needed and the battery would go down while driving. The belts were not making a noise, so I thought it was a bad cell in the battery, until I had it checked.

Cass

 

Let's start at the beginning: Other than the light, are you having problems with the battery dying or anything?

In the old days the battery or alt light was some sort of a voltage balance circuit. If the circuit went kerflooey, that would cause the light to come on just like if the alt was going bad. You'll need an EE to explain the theory of it, but suffice it to say that if the alt & bat test out good (and aren't dying on you), the problem is likely in the warning light circuit.
-dave

 

no im not everything is ok starts fine

 

Hmm... One thing about testing alternators, especially when the light comes on and goes off whenever it wants, is that when testing them on the bench, they aren't running at the same temp they do under your hood

The regulator (or the stator, or the rectifier bridge) can have a bad connection, and as soon as it heats up (or cools off) the connection breaks or changes resistance and causes it to not charge.

The light on newer vehicles is driven by an output right off the regulator, if the regulator is driving the light, it thinks something is wrong.

Since you've already checked everything else, check your grounds. The engine-to-battery, engine-to-body, and body-to-battery all need to be solid and making good connections.

Other than that, a slipping belt can do it, but it sounds really like the regulator is going out.

Without really checking everything, get a good volt meter, and check what the voltage is when idling. It should be above 14 volts, but not above, say, 14.7 volts.

If it's way lower than that, or way higher, the light will come on.

One quicky way to check the alternator is, turn on the interior (dome) lights while the engine is idling. Turn off the key, and if the lights do NOT dim, the alternator wasn't working. This might be a good test to try when the battery light happens to be on, but check it when it's off too.

Report back... we'll work with you on it

 

Good advice. Voltmeters are cheap as dirt, so if you don't have one, get one. Very handy. When you see the light on, check the voltage across the battery posts as Krewat indicated (car idling).

I should have said to check the batt voltage in my first post too. Good catch.

-Dave