I am driving a 2000 ford Ranger with a 2.5ltr 4 cyl engine. I think I am having some alternator issues. In the mornings the truck starts fine, but the voltmeter drops off and the battery light illuminates. After about 10 mins or so the voltmeter comes up to normal and the battery light goes away. I drove the truck to my mechanic, but he could find nothing wrong with the alternator or the battery. The voltmeter and battery light were operating normally at this time.
My first thought is that the belt is slipping. I have a ford van that does the same thing but for only a couple minutes, then everything comes up to normal. Check your belt and belt tensioner and also make sure nothing in on the belt like oil that can make it slip.