Hi all, 1st post here. Truck is an '07 f150 4.6 with approx. 95,000 mi. A couple weeks ago I installed a new battery after the old one failed. I had it tested. After installing new battery charging gauge on dash showed battery wasen't charging so I brought the truck into dealer who diagnosed a bad alternator & installed a new one. Here's the problem. On at least 4-5 occasions the alternator gauge has pegged all the way to the right showing battery is overcharging, then battery light on dash comes on. For example it did it yesterday. I pulled over, shut the truck down & it started & ran fine for the rest of the day. Same scenario every time. I'm assuming that the serpentine belt if fine as the dealer didn't recommend a new one. Truck is not throwing a C.E.L. Does anyone have any ideas on what's going on here? Thanx for your help.

 

Maybe a bad voltage regulator? In any case, the dealer who installed the alternator needs to fix this.

 

Isn't the V.R. inside the alternator?

 

I believe so. Sometimes "new" parts are bad out of the box.