Alternator/Electrical Question

[rtstrack]

Ok I fixed the noise problem. Apparently the black wire wasn't grounding the alternator through the voltage regulators bolt, but it was actually the voltage regulator that was being grounded through the alternator. Anyways its back up and running but with the engine at idle the battery only tests at 12.0. An additional piece of info is that the voltage gauge (on the dashboard) reads slightly less then 12 when it starts up. When i turn on the fan & lights it will drop down to 10.0, but then when i turn them off the needle immediately bounces back up to 12. So I'm assuming that the alternator IS working, because if it wasn't, then wouldn't the needle stay at 10.0 and not return back up? I am now assuming that I have an undersized alternator. I swapped out the alternator with the EXACT same one that was in the car (got it from NAPA), it was just some generic ford alternator. The sticker on the side of the alternator reads 34amps @ 2,000 rpms and 72 amps @ 7,000 rpms, these are aproximately the numbers I remember seeing before I installed it, give or take an amp or two. Rick, I have lights, fans, msd, stereo. No idea if the pulley is undersized or not. Not fuel injected. Hope this helps