i have a problem with my 95 Maxima GXE.. im not a genius on cars but the battery light and brake light comes on at the same time.. and im not sure whats causing this to happen.. i thought it was the alternator at first.. but my friend told me that disconnecting the battery while the car is running is a way to test if your alt. is good.. and it passed.. i need help on this..

also my audio systems also meesing up as well.. i have the factory bose player, but it seems to work well.. when im stopped but as soon as i accelerate the audio cuts off

 

Typically that is a sign that there is a problem with your alternator. If you have a multimeter, check to see what the alt is putting out. Check the voltage while the car is off and while the car is running.

 

I had the same problem. it turned out that my alternator was bad

 

+1 ALTERNATOR

 

how long would the alt. last.. its been doing it for about a month now and its goes on and off a lot

 

it will last until the worst possible time for it to fail.
Been there, Done that.

the "pulling cable off battery to see if car dies" test is not exactly accurate. in your case you have a bad diode or rectifier in the voltage regulator. So, even though you are putting out voltage it is not neccessarily the correct amount nor is it neccessarily regulated.
In your case I'm 95% sure that the voltage regulator is bad so you will need to replace it ASAP unless you like getting stuck.

 

 

+1 on the alternator.

I had to replace mine twice this year. I had a new one put in back in February then another one in July. I hope I don't have something else wrong that's taking them out. The good news though was that the replacement was covered under warranty from the shop that put it in.

If you have a multimeter, measure the battery with the key turned off. A good battery is usually around 12.5 volts. A little less is ok. But if it's like 2 volts or more, then you do have a bad battery.

Now start the engine. With a good alternator, I would expect the battery voltage to be about 14.5 volts or so. If it's not, then the alternator is bad.

 

like everyone else has said..its the alternator...the reason why your car is running when you pull off the battery is because the alternator is essentially overcharging. Overcharging your battery will cause the battery to die and then corroade n maybe even explode. You do NOT want battery acid over your car..thats just asking for all types of trouble. You're one of hte lucky ones whose alternator overcharges instead of not charging. But again, replace the alternator.

 

Alty is failing.

 

everyone is right, its the alternator. My car lasted for abt 30 min before my battery died.

 

thanks to everyone for tips..that battery and brake lights were really bothering me.. gotta get that alternator changed with the quickness