I have been having a problem with the voltage dropping on my '91 Trans Am while the car is idling. I have a battery that's less than a year old. I have also disconnected the battery while the engine was running and the voltage dropped dramatically on the gauge when I started using accessories like the windows and headlights. So I went and replaced the alternator with a brand new, non-remanufactured unit from Checker. However, the problem persists. The voltage drops to around 10 on the gauge. I have noticed that the passenger window refuses to go up or down when the voltage drops too low, yet the driver's side window works fine. My radio never misses a beat and the headlights flip up and down with no problem.

I went ahead and disconnected the positive battery cable and put the positive lead on my multimeter on the battery and the negative on the cable and it seems to be drawing 7.5 to 7.6 volts. Switching it to amps it seems to be drawing 7.2 to 7.3 milliamps if I'm reading correctly.

I'm not an electrical expert, so any help or suggestions is greatly appreciated.

 

Do not disconnect the battery cable when measuring Voltage.
Just measure across the 2 terminals. When measuring Current (Amps) you do need to put the Ammeter in series with the battery or you could get an Amprobe and clip it over
one of the battery leads.

I hope this helps.

BTW 7.3 mA seems way too low to be correct.

 

I forgot to add that I did test the battery voltage across the terminals with the car shut off and it was reading 12.2 to 12.4 volts.

Thanks for the help. This is pretty puzzling.

 

that sounds right, my voltage drops like that too and ive owned the car two years and have yet to figure it out had the battery load tested and it seems fine same with the alternator when i first got the car i was suspecting the fuel pump... then i found out it was a mechanical one good luck anyway

 

I just measured the voltage across my battery and it's 12.4 off and 14.4 V running. I think that's about right.

You have to have something in you system drawing too much current in order to be pulling the voltage that much.

Not sure how else to help.