1997 F-150 4.6L has a severe stumble when i turn on my headlights?? It will be running just fine and when you turn on the head lights you get an immediate drop in RPM by like 400-600 rpms, before it finally recovers. It happens at idle speeds as well as higher engine speeds. It acts like its going to die on me and then it will recover and be just fine. It only happens when the switch is turned into the on position, and it does not matter if its just the parking lights or the head lights too, and if you wait a few seconds before turning on the fog lights it will do it then as well. ANY INFO?? I am at a complete loss here so any info would be helpful.

 

I think I would get the alternator checked out. The voltage regulator is inside the alternator I think. they usually are.

If something were shorting out to give that much of a symptom, I would think a fuse would blow.

 

thanks for the advice i did swap out the alternator after making the post just cause i had a spare laying around, took care of the problem. Thank you