[mustangman65_79]

It's not your alt. Your guage moving with your RPM's is normal. Till u hit about 2,500 RPM's, your alt isn't doing a full charge. Ever got a jump start from some one, and have them rev the motor up? It's to get a better charge.

If all your lights work, and everything else, then your ok. I'd say it's your starter soleniod. This is located, usally on the left side of your firewall, on your fender. It's black, and has both your cable from your batt, to your starter. You'll also see either two, or one small wire going to your soleniod. This comes from your ignition switch(where your key goes in). Find a screw driver( if there is only one wire), and cross from your batt wire, to the small wire. See if it starts(tries to). If it does, u have a bad Ignition switch. If not, then it is the starter soleniod. U can bypass the soleniod by crossing from your batt, to your starter cable. Watch out for sparks. If this doesn't work, it's your starter. But u would have heard it going out beofer it did, usally.