I was ideling talking to some friends for a while last night, and on my way home I was at a light and I was ideling at about 700rpm and my battery light came on, but as soon as I tapped the gas peddel it went away, my lights were dim but as I was driving they became brighter. When I got home to battery read 11.7 volts with the car off, with the car on it read 10.8 while it was at idel and the battery light was on. Also, sometimes my idel will be at 700rpm or 1100 rpm, today it felt like hitting 1100, and the battery light was not on at idel either, I got home and the battery read around 12, and with the car on it read about 13.7-13.9. Do I need a new alternator??? It is a 1991 Honda Civic

 

You may need a new alternator. First check whether the belt is loose and slipping.

 

I recently got a new belt, and it squeaked so I tightend it, maybe I need to adjust it again?

 

Okay... Just went out again today and my alternator is working fine, I tested the battery while it was running revved it and the voltage went up.. Heres my theory.. I was sitting for about 1h cant remember to well.. had my headlights on and the car was being fussy and ideled at like 7-800 the whole time, could it be possible that the because I was ideling so low and my lights were on that my alternator wasnt putting out enough charge to keep the battery charged... So then I get to the light and my battery is has been drained a bit so my alternator had to work overtime to juice it up causing the light to come on.. That sounds reasonable...

 

You can test your alternator using a voltmeter or multimeter. At normal idle with high electrical load (e.g., high beam headlights ON), the voltage between the two battery terminals should not drop below ~9.5V.

 

sounds like the regulator inside the alternator is going out.