Amp light always on.....


Old 04-20-04, 06:15 PM
Thread Starter
Join Date: Oct 2002
Posts: 161
Amp light always on.....

Hello folks,

I have a '93 Olds 88 - 3.8 Driving along and my 'Amp' light comes on. I took my multi-meter and measured 12.6 DC volts with the car NOT running. Started the car and measured 12.3 DC volts.

Didn't think my alternator was working so I got a new on. Put the battery on a trickle charger until it was 'full'.

Started the car and the amp light was off. I thought everything was OK but after a few days my amp light is back.

Checked and re-checked every connection and cleaned terminals....still reading about 12 DC volts whether the car is running or not.

How many DC volts is a fully charged battery?

Anyone got any ideas?

Appreciate any help.

Thanks, Trip
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Old 04-20-04, 06:37 PM
Desi501's Avatar
Join Date: Oct 2003
Location: Boynton Beach Florida
Posts: 2,207
Sounds like you cooked that new alternator. A fully charged battery is 12.7 volts. Those high output GM alternators are very fragile when over worked. The quality of the reman and the amount of charge in the battery are critical. Alternators bought at the discount stores are usually very low quality. I would use a Delco Reman and nothing else. Next, be sure you recharge your battery fully before starting the car with the new alternator. I would also have your battery tested as it is possible for it to call for too much charge and overload the alternator that way also.
Old 04-20-04, 06:38 PM
Join Date: Feb 2004
Location: So Cal
Posts: 248
noraml batt voltage ...... 12.6 fully charged.

Normal charging voltage should be between 13.8 to 14.3.

Sounds like you've got a bad alternator.

Old 04-21-04, 03:54 AM
Thread Starter
Join Date: Oct 2002
Posts: 161
Thanks for replying. Yeah, I knew the measured voltage should be higher than 12 volts DC when the car is running.

If I fried the alternator that means that the 'Amp' light would never go off? Sometimes, at low idles and speeds, it goes off.

Does that make any sense?

Old 04-21-04, 09:02 AM
Join Date: Feb 2004
Posts: 64
have the alternator tested at auto zone or the likes (for free)
I`ve had alternators that hovered between the edge of charging and not
(diode going bad). Also (as mentioned above) have your battery load-tested
at auto zone. How old is that battery, has it had a few discharges over the years ?
my 2cents
Old 04-21-04, 09:52 AM
Thread Starter
Join Date: Oct 2002
Posts: 161
The battery is about 3-4 years old. It has never been run down completely. The car has been running off of it for a couple days and it still registers about 12DC volts.

I've put it on a trickle charger before i started it after I put in the first alternator. It is on the charger again right now.

What is 'Load tested' mean?

Old 04-21-04, 10:41 AM
carguyinva's Avatar
Join Date: Nov 2003
Location: Shenandoah Valley
Posts: 1,147
load testing...

load testing (high rate discharge testing) is a method of evaluating a battery's ability to supply power for a short period of time. it is done with a carbon pile...a device capable of draining large amounts of electricity from the battery very quickly. load testing is hard on batteries...esp older ones. the more modern and most accurate way is thru conductance. a conductance tester forces a small amount of voltage thru the battery, thereby testing it's internal resistance. this takes very little power to accomplish and can test discharged batteries as well. from my own experience, most parts places don't load test them correctly so it would pay to ask what method they use (if they could even tell you that).

in other can take a weak battery and it will pass a load test if you use the wrong load value (measured in amps and not always given on the battery). to do conductance testing...all you have to have is the CCA rating of the battery and they ALL have that...either on the battery or in the catalog

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