This is my first post here so hello to everyone. I have a 2002 f250 crew 4x4 lariat with the powerstroke diesel and the day before yesterday i noticed the battery light stayed on when i started it up in the morning yet it seems to go out as soon as you get above the 1200-1500 rpm range. Then when you come to a light or it idles the light keeps coming back on.The batteries were replaced in july so i doubt its them. I'm leaning towards the alternator being the culprit but with todays vehicles,who knows?Also i notice that when its humid out or if its damp,the door ajar light will stay on also but this really hasnt been a big problem....just more of an intermittant nuisance than anything else. i'm looking not to take it to a garage as i want to try to diagnose these problems myself and try to save a few bucks while im at it. I work union so im unemployed right now.Any answers/help would be greatly welcomed.Thank you

 

Welcome to the forum! I had a similar problem w/ my battery light on Monday. It came on when i started the truck & left the office at 5 and stayed on. We went to eat dinner, then the rodeo, then home. The light stayed on while the truck was on and didn't have any problems starting. Tuesday morning, the truck seemed pretty hesitant to start. I went to the coner store to get a drink on the way in to work. When i got back in, it barely started. I went straight to the dealership (only b/c it's still under warranty) and they diagnosed it. Just as i thought, the alternator went out. So they replaced that. I was running on the batteries only. They checked the batteries and said they seemed fine but put 2 new ones in anyway. Had it back by lunch. It would've cost me $834 if i had to pay for it. Thanks God for the warranty! The truck is an '06 w/ 18K on it. I asked why it went out soo early and he said it's an electrical part and you never know when they're gonna go out. My guess is that it's your alternator, possibly the batteries. The owners manual says that when that light comes on it means the batteries aren't being charged correctly (ie alternator bad).Go to an Auto Zone, O'Reilys, or some place like that and they'll check your batteries and alternator for free. You'll know what's bad and can get a reman one at a good price. Dealership charges $250 just for the part. Parts store will sell a reman for around $125-$175 probably. Have them check it and see what you find out.