Bad alternator?

I just bought a new car, and got the system all hooked up yesterday.  I was driving around and I noticed that whenever I was sitting at a stop light the battery gauge would go down to the last bar (around 8-9 volts).  When im actually driving the gauge is higher up.  The car is a 86 Cavalier and it has a 90 amp alternator, it use to run the AC but that is no longer hooked up.  Its possible the problem is in the battery gauge itself, its a digital dash snd doesnt work to well, but the battery gauge seems to be ok. Could this be a bad alternator, I dont want to buy a brand new alternator becasue ill be happy if this car lasts me the winter.

Could be the system is simply too large for the alternator, or yes it could be a bad alternator or voltage regulator.  Could also be as simple as you need to replace the belts (not a bad idea for a 19 year old car in any case.)Support the12volt.com

When I drove it today when I was stopped the amps would actually cut out. The alternator on my previous car had a smaller alternator and that never happened.

A quick way to check your alternator would be to start the car and with the car running, disconnect your battery.  If it doesn't have enough juice, the car will die.  It's not conclusive but it's a quick way to find out of your alternator isn't cutting the mustard anymore.

on a older car like this I would say you are alright to disconnect the terminal frrom the battery but never try this on a newer vehicle.    could cause massive problems espically if you pull the ground side2009 0-1000 Trunk WR 154.0DB 2009 1001+ Trunk WR

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I had to do it last week on my '04 F-150.  : )  The alternator on the wife's mustang went out on the freakin' freeway.  Didn't have any choice but to switch batteries with my truck and leave my truck running the whole time.  Worked like a charm.  Or atleast good enough to get us to a place where I could switch out her alternator real quick. 

My system includes a Memphis 250W amp with a 20A fuse, running two orion subs and a Power Acoustik amp with a 40A fuse, 525W max, not sure of the rms, running the speakers. I have 4G power wire from the battery, stepped down to 8G to the amps. I never had problem on my previous cavy, a 91 with a much smaller alternator. The lights would dim on that a little, but the amps would never cut out even after ildling for a long time. I wish I would have kept that car, this one is a piece of junk, if it turns out to be a bad alternator I think im just going to get rid of it.

Like I said before, get the charging system checked, and replace your belts.Support the12volt.com

My friend has a alternator that will fit the car, so we are going to swap them out today and see if it solves anything.