View Full Version : batt light is on. with a new alternator???

08-04-2010, 04:36 AM
i own a 1991 toyota celica 2.2 and last night on my way home my batt light came on. i pulled into my drive way poped my trunk open unpluged the negative battery terminal, car dies. so it must be my alternator right?. so today i picked up a new alternator installed it started my car and the battery light is still on. so with the car running i wanted to check if i had a faulty alternator, so i unplug the negative terminal and the car keeps running. so i unplug the positive terminal and the car is still running strong, i rev it it wont die, but the battery light is still on. so i know the new alternator is charging because it stayed running after i completely unpluged the battery.. so wat the heck is causing the batt light to stay on. could it be a wrong alternator?

08-04-2010, 08:09 AM
could be a faulty alt or weak battery, the autoparts stores do a free starting and charging test

david in germany
08-04-2010, 10:34 AM
Charge the battery, If it is low from the other alternator it could be still giving you the light (it is also hard on an alternator to charge a completely dead battery)

08-04-2010, 12:23 PM
2x on getting the electrical system checked free at an auto parts store with their equipment. I think you will find the source of the problem by having it checked out properly first.

08-04-2010, 01:42 PM
also be sure to check your wires, the battery ones and the alt wiring

08-04-2010, 06:27 PM
ok thanxs guys,

08-04-2010, 06:28 PM
I agree with everyone, but especially David. Even though you replaced the alternator, that doesn't mean that the battery is charged. Try charging the battery, and if the light stays on, have the parts store test the battery and alternator.

08-04-2010, 07:25 PM
well bought a new battery installed it and the light is still on, so i wanted to make sure of something so i disconnected the negative terminal from the batt and this time the car died. wat the heck. before i got the new batt i was able to disconnect both batt terminals and the car would still run know it dies. could it be a bad alternator

08-04-2010, 07:47 PM
if you disconnected the batt and the car died its the alternator.

08-04-2010, 08:33 PM
thats wat i figured. i took it to get tested and it was charging at 12 volts wich isint good.. but the funny part was that the batt light was on when i got to the test shop. i turned off the car then they came out to test the alternator. i start the car the batt light is off and they said it was charging properly. so im comfused at wat the heck is going on so i get in my car, i start to drive the batt light comes on i call the guy over, he checks the alternator and its at 12v. so i figured that once the alt get hot the light come on. so im dropping it off later today, and ill see wat happens

08-04-2010, 08:36 PM
might be a parasite then

08-04-2010, 09:14 PM
I'm going to say Bad Alternator..when my original Alt finally went after 19years I went and got a new one...that one blew the voltage regulator in a day..brought it back got another new one...after a month the batt light would come on periodically for a few seconds then go away ( at the same time U can watch the volt gauge drop on the dash) until it got so bad to where the Batt light would come on at cruising speed, id have to give it a good hard rev, that would get the Alt goin again.. So I brough it back again...Another blown voltage Reg..

Then after that I find out that they're not "new" alternators they are just Remanned ones..So I said fack you got my money back, went to another shop and got a Brand New Alt..and havent had problems since...

Long story short Make sure your getting a NEW alt, not some Remanufactured POS

08-04-2010, 10:46 PM
ok thanxs, i dropped it off, and ill pick up another one tomorrow, lets keep our fingers crossed this one works

08-05-2010, 12:08 PM
I've used remanufactured alternators for years with very few problems. A new alternator can have a similar failure out of the box, or shortly afterwards, that a new alternator can have. Things just aren't made today and fully inspected to run for a long time anymore.

For reference, the "battery light" is an indicator of current flow only, not of the condition (charge level or voltage level) of a battery. It runs based on the a diode. Current running in one direction (say towards the battery, or charging it) flows through the diode without detection (no light on). Current flowing the opposite direction (away from the battery, or discharging the battery) flows the opposite way through the diode, which the diode now detects and activates the "battery light".

Most often, when a "battery light" comes on, the problem being detected is something other than the battery. A battery that is dead, or nearly so, that can no longer maintain a proper charge, draws from the alternator, and the current is flowing towards the battery, so the "battery light" does not come on. But a volt meter would indicate low system voltage in this case. It is best to have both a "battery light" and a volt meter in a car, because either one on its own doesn't tell the whole story of what is going on, but both together do.

08-06-2010, 06:54 PM
so i finally installed the alternator, changed the battery terminals, started the car, and so far so good. the batt light is gone, but im still keeping my fingers crossed. but thank you all for the great advice i received, this issue was starting to drive me crazzy :)

08-06-2010, 08:47 PM
I'm glad you got this figured out. 93celicaconv made a good point about the diode, didn't even think of it :11doh: