I have a 2008 F150 FX2 sport. The battery light comes on. I've had it checked with a mechanic. The alternator shows good and it has a brand new battery. Before I replace the alternator I was going to research what else it could be.

 

There could be something else wrong with your alt besides output. I'd remove it and have one of the box stores bench test it. If bad, replace with a Motorcraft reman. If good, check grounds, fuses, and condition of battery cables.

 

Thanks. I'll have it checked out.

 

My battery light finally went out after new alt. Had to go through 2 because of the pickiness of the electrical connection device that for the life of me I cannot remember the name of right now. Anyway I think I recall my alt checking "good" but was whistling like crazy so decided to change it and batt light came on after the new one and went away on the second one