I have a 2001 F250 5.4L V8 with about 158k miles on it. Just bought it a few weeks ago. The alternator went out the first week and I replaced that with a new unit. PCV valve was making a loud noise and replaced that last night. I have had it tested at 2 separate places that both said my alternator and battery were operating fine. I have been having an issue where when I first start the truck in the morning the dash lights, airbag light and headlights will dim for about 10 minutes. The battery gauge on the dashboard will move slightly up and down in a jerking motion. I'll run the truck on the road for a few minutes and it will all stop, then when I park it it will do the same thing on and off. There is a small gray harness on top of the alternator that was dry rotted and when I replaced the alternator it wont clip, I have a new one on order and fixing it this week. I'm concerned that something electrical is going on that is not the alternator. Also the battery light will dim in and out but I think that is from the loose harness. Any idea why the headlights are dimming? I also ordered a new coolant seal cap because the one on there is not closing and allowing enough pressure to build up. I don't think that is related. Any help would be appreciated!

 

Fix the obvious problem with the electrical connector first, before worrying about if anything else is amiss. The glaringly obvious problem will obscure the ability to see anything else.

 

Don't trust the dash gauges on your F-250 or any modern vehicle. Sadly most all modern vehicles massage the dash gauge readings thru the PCM, providing no more information than an "idiot light". Use a scanner or DVM to obtain accurate voltage measurements.

 

Replaced the alternator and the battery 2 days ago, just broke down on the highway same issue as before battery light was on and I lost all power and the truck died. I'm at a loss with a brand new connector , new battery and alternator. Is this some kind of wiring issue ?

 

Other than "guessing and replacing", have you done any actual troubleshooting? Have you checked the "A" circuit?

 

Get a meter or bring it to a mechanic... 12.7 volts fully charged battery.engine off . 14.4 or so across battery running engine...