I started to notice my battery light comes on during a hard acceleration. So I have been keeping track of it. When the rpm's hit 3200 and above the light comes on bright but never at any other time. I put a volt meter on it and I have 13.4 volts at an idle, as the engine revs up the voltage climes to 13.9 then when it hits the 3200 mark voltage drops right off to 12.4. It seems like a regulator issue to me. The parts store says my 5.4 has an external regulator is that so or is it built right into the alternator?

 

For better help,we need the year and what truck its on.

 

My truck is an 04 F250 with a 5.4 gas engine.

 

Check the belt and idler pulley. Sounds like belt could be slipping at higher rpm.

 

No squeal like a sliping belt. The light comes on bright when it comes on not dim or flikering like a sliping belt or worn brushes, thats why I was thinking regualor.

 

i have a 01 f250 5.4L and my battery light comes on at times also. sometime it stays on sometime its blinks. it started about a year ago, i took the alternator to have it bench tested 2 different times at 2 different places and both times they told me it was good. i have good voltage at the battery also. i think i have a loose wire or some sort of short in the dash light because i never had a problem starting my truck it never died on me and like i said its been doing it on and off for at least a year. and not every day either. it might do it a couple days in a row and then it wont do it for a week or a month or even a couple months before it does it again. i cant seem to find out why it does it but if you figure out yours let me know please

 

I talked to a tech at the local starter/ alternater repair shop. He thinks I have a short in a stator winding or somewhere in the alternator itself. He said that when a elctronic regulator fails it stops working completly and would not be related to rpm's. That makes sence to me, electronic ignitions either work or don't work there is no in between.

 

Sounds like a reman is due