funny stuff happens when the car is in drive,headlights on ,stereo,heater going,and foot on the brake the volt meter on the dash drops down to the red zone then goes back up when I start driving again.I did the isolation test on the battery and it showed no draw of any kind on the battery when it's just sitting but my battery died after sitting for 3 days in the garage with the alarm off.Could I possibly need a bigger alternator due to the aftermarket stuff on the car (700watt amp,headlight upgrade,alarm system with remote start) the alternator tested fine at auto zone and the battery has 14vdc when the car is running so it seems like it's getting a charge do I need to upgrade to a 200 amp alternator????

 

is your deck running straight from the battery?

 

just the memory part other wise it's switched from the ignition

 

You might be able to help the situation by adding a 1 farad capacitor to your stereo system.Im runnin a 760w amp and after I installed the capacitor my voltage no longer drops. Mine cost about 90 bucks I believe.

 

Bad
I have a 1 farad capacitor that i'm going to install just haven't got around to it yet also just noticed something odd with the lights on,stereo,and heater its measuring 14.2 amps as soon as it goes into drive it drops down to 12.1 that seems like a huge draw just for going into gear .nothing in the tranny should pull a 2 amp load should it???

 

also thanks for the help guys

 

its actually volts, not amps. and the volts drop down when you shift into gear because the RPM of the motor also drops, thus reducing the RPM of the alternator.

 

http://www.mean-green.com/products/alternator.html

Tom Piper

 

Is it the original alternator? How old is it? It might be starting to go.

Our cars have a 140 amp alternator. You should not need a bigger alternator. You might however have a bad alternator. When Auto Zone tested it, their machine only check to see if it produced voltage. It has no way of knowing if it is putting out the full amperage. You might want to call around to see if you can find a place that can do a full test on it. Voltage and amperage output.

 

it's only 6 moths old but it looks like it's charging i'm getting 14.2 volts at the battery when it's running

 

What's the voltage across the battery drop down to when you crank the engine? It may be that the battery is old and won't take a charge.