Originally Posted by Richard D
It is very possible that the new alternator is faulty.
It would also help to know what year make and model your vehicle is.
And your post is very vague when asking for tech help the more info you can suply the better we can all try and help
I forgot to put that info in there didn't I.
2002 F150 Supercrew with the 4.6.
If it is just idoling it runs off the battery only. When a start from a stop or rev the engine the battery light goes off until it goes through each shift the more the battery light comes on then it just runs on the battery it's self.
I'll try to make it get the alternator checked.