I have a 2005 Fx4 automatic and during hard acceleration when the rpm's get around 4500+ the battery light comes on, once the rpm's go down some it goes off again. Has anyone else ever seen this?

I don't know if the alternator is not able to keep up at higher rpm, or if it's producing too much voltage.

Thanks
JK

 

my 2000 did it but it stoped for some reason

 

Check your tensioner for its amount of travel (you are also trying to determine if the belt is stretched).

If tensioner is strong and belt is good, it'll be new alternator time soon.

High rpm Volts light usually means the brushes are worn down to the point that spring tension can't maintain brush contact = replace alternator.

 

i dont think that brushes are on a alternator since they produce ac voltage, if it were an old style alt(generator) then yes i believe it has brushes. i think im write but could be wrong

 

I had the same problem on my dads 2000 F-150. When we were pulling my grandpas trailer through Kentucky (kinda hilly), that light would come on when it down shifted real low.