Electrical Trouble!!!

I have an alternator that is only a couple of months old. Last night, when I left my friends house, my check engine light came on and my alternator gauge said it wasn't charging. Why is this? It has read like this before but all I had to do is run the tranny in first and RPMs up to 4 grand, then it would be normal. Please help, it's my D.D.

my first thought would be that you have a loose wire somwhere. if not that thake the jeep to where you got the alt they should be able to test it somtimes youll just get a bad one

I got it fixed. It was a loose connection and thanks to a gum wrapper, my alt is chargiing.