charging system problem

well staright to the problem.. i own a 97 3000gt sohc model and the alternator went out about a month or so ago. I replaced it and the new alternator went bad in a few week so it was a defective one... so now i installed another one but now the battery gauge does seem to stay at a constant ready... i already got the battery and the alternator checked out and everything checks out ok... but in the mornings when i cold start it.. the gauge reads like its supposed too... but once i have been driving for a little while and the car is warmed up... the gauge reading will drop slightly.. and when i come to a light or just idling... my dash and the lights start dimming.. but once i take off the lights light up again and the gauge reads as it should at first i thought the gauge might be unaccurate but the lights dimming prove that wrong... i have check the belt tension and all the alternator wires and i have run out of ideas... the alternator is good and the battery is good and the gauge is good... but i know there is a problem.... it didn't do this before the alternator went out...

Check your cables.

All the 3S's i've owned have done this. Raising the idle by turning the BISS screw is known to correct the problem.

yea all the cables are good and i have gotten the alternator checked and it's good too..... well like if i would adjust the screw.. then my car would idle higher so then the alternator will stay up right..... but like i always have a sounds system in it... and like before i replaced the alternator... the bass would hit and the needle or lights wouldn't dim at all.... now the needle just drops in voltage each time and my lights dim too.... would that solve that problem too?? yea but also when the car is cold... it reads like it's supposed to.. but once it's warmed up... the gauge drops

How do you know your battery is good? Did you have it tested? Now that it's not 4am I remember my VR4 stopped doing this after I replaced the battery.

yea i got the battery tested and they said it was good... but wut i did notice was that when i removed the battery... you could see on the side of it that like some of the fluids had came out of it... but i also borrowed a new battery cuz my friends works at a place and it still did the same thing... but it was a cheap battery though .... you think an optima would maybe fix this problem.... but i was also thinking...maybe the alternator is charging but maybe the built in voltage regulator isn't any good???? is that possible???

Well the alternator either wouldn't charge or it would overcharge if the regulator wasn't good...what's it charging at? do you have a voltmeter?

yes i have a voltmeter..... and i have proved that the stock gauge is a lilttle unaccurate....b/c the gauge will be reading a hair below the 12v line and the volt meter will say its at 12.5 volt.... i am starting to believe that your right... it's normal... but i just want to make sure you know... i don't want to get stranded because i have already once before lol...

yes i have a voltmeter..... and i have proved that the stock gauge is a lilttle unaccurate....b/c the gauge will be reading a hair below the 12v line and the volt meter will say its at 12.5 volt.... i am starting to believe that your right... it's normal... but i just want to make sure you know... i don't want to get stranded because i have already once before lol...

Stock gauges are all inaccurate...but what's the voltmeter read with the engine running?

the voltmeter read around 12.5 to almost 13...

thats still rather low, i usually charge at 13.5-14.0, as most other cars do...

the voltmeter read around 12.5 to almost 13...

Yeah there's a problem, should always stay between 13.5-14.5 when the engine is running. Since you just replaced the alternator I would lean towards the battery if the connections are all good. A defective alternator is a possiblilty however.

What is your battery voltage when the car is off cuz if your only running 12.5v to 13v with the car on and alternator charging it then it seems like your battery is going. 100% battery charge from a new batery is 12.65v to 12.68v. A 75% charge is about 12.45v and when it gets to be below that voltage your battery will start going very fast. You can check your static voltage (voltage from the battery when the car is off) by doing the same thing as if the car was on. Also make sure that your connections on your alternator are tight cuz even if the alt. is brand new it won't charge to full potential if the connections are loose. Check the battery connections as well, and check for corrosions on the terminals cuz that can cause resistance in the system causing the battery voltage to not flow like it should be. One other quick test you can do is a static discharge. This is when voltage is "leaking" out of the battery case its self. To do this you take your negative lead of your voltmeter and place it on the neg. battery terminal, and take your positive lead and kinda poke around on the case on not just the top but all over. If you have any voltage readings this means that the case is getting old therefore you should be looking for a new battery. Let me know what you get. I hope this helps you out .:)