After 3 blissul years of owning my 1994 Coupe with no mechanical issues, the odds seem to be catching up to me. Last night I was driving home from our Corvette Club meeting the battery/alternator light came on. (When my Optispark died two weeks ago it was the first indicator but a lot of other stuff went with that). Car was still running fine and I was able to get home. The car even started this AM with no issues but the light is still on.

1. I have a brand new battery
2. I have a new serpentine belt
3. The tension on the belt is fine and the alternator is turning.

Is there any other reason that the light would go on & stay on other than the alternator? I do not have any real diagnotic tools other than taking it to the shop that does our work.
Thanks for your feedback.
Bill

 

Bill,

you can check to see if the alt. is charging with just a screwdriver. Touch it to the center bearing cover on the back of the ALT. while the car is running, there should be a noticeable magnetic pull on the screwdriver blade. If so, the alt. is charging, and the problem is somewhere else. Ber careful not to touch either of the terminals back there whene doing this if they aren't insulated, or your screwdrive will miraculously transform into a arc welder! Not real good for the rest of the cars electrical system when this happens, either! Also, most of the major auto parts stores have a portable charging system & battery checker that they can roll out to the car if you can get it there (better if you know someone at a parts store whose head isn't firmly tucked up their hindquarters. You can usually recognize these guy's by asking a few simple questions, and seeing if they can answer without looking in the computer, such as "Do you have a universal muffler hanger"? Oh yeah, if they tell you they don't normally stock valve covers gaskets for a small block Chevy, RUN, don't walk to the nearest exit and find another parts store! (Don't laugh, this actually happened to me at a local Autoz#$e, another good one was the kid behind the counter at SuperShops who told me "I didn't realize Chevy made a Big Block"!!!!!!!

 

I only ever had the alt go out like that in a car once.

In my daily driver that happened, no warning, the light just came on.
Took it to Autozone, they tested it (for free) told me it was very weak (don't remember specifics).
I put a new one in from there, and it lasted me the rest of the life of the car (about 5 more years).

 

The battery symbol light comes on when the alternator is not charging the battery. Your voltmeter will also tell you the same thing. Engine running, the normal voltmeter reading should be 14.3 volts cold, 13.3 volts hot. Holding a screwdriver against the alternator merely tells you that the alternator has field current, not that it has charging current. Just look at the battey voltage, that will tell you if the alternator is charging the battery. Get your alternator checked at an auto parts store. My money is on a defective alternator.

 

Thats an excellent tip.
Another quick and easy way is to measure the voltage at the battery with the motor off using a multi meter. Then measure it while someone starts the car. There should be an immediate jump in voltage to about 13-14 volts and should stay there with the motor on, and should fall back down to it's previous voltage when you shut it off. If not the battery is not being charged.