first mustang, few problems.
 

just bought my first mustang, its a 1989 mustang gt 5.0 manual. fixed most of the minor problems except for a few. the only major one is that my alternator gauge sits at about 9 volts. ive checked the volts going across the battery with the car off, which read 12.3 volts. at idle the battery only read 12.6 volts. the gauge goes up while driving and up in the rpm's. is this a bad alternator?

Yes, the alternator is bad. The volts at the battery while the car is running should be around 14 volts.

Alternator.

have the alt tested:D

at idle mine sits at about the same maybe a little higher 12.9-13.1 and my alt is fine, but i've always had charging issues. no one can seem to figure it out. :(

do you have underdrive pulley(s)??