89 GTA alternator ?

I recently noticed that when I start my TA, the volt meter shows on the discharge side (9volts or so) for a couple of minutes then goes goes to the normal 14volts or so. I've only noticed this after it has sat for awhile(over night or through the day) I had the charging system checked and they said it was good. Voltage regulator maybe going bad? Any help or comments appreciated.

Guitarz

if they said it was good, they can be wrong. Something stupid like a diode trio or something, i'm not really sure though. As long as it does charge the battery, cool, if it doesn't then stick a new one in there.
Jake

Thanks for help. I replaced the alternator ,and it seems ok now. I will keep watch on it. Thanks again. Tom