I have done some research but nothing I have found has helped. A few months ago, my battery wouldn't stay charged, so I got a new alternator and put it on. Ever since then my battery keeps surging. Going from half way all the way to the red at 18v. It does it while going down the road and while idling. It blew both headlights today. Any ideas on what would be causing this?

 

Bad alternator. Sounds like you bought a cheap reman and it has a defective voltage regulator.

 

When it comes to these alternators(and really any electronic part in these trucks) only go motorcraft. These trucks really really picky. If you got an Advance Auto one, the new and remans for these trucks suck. I don't know what the problem is, but the only alternators we consistently had returned were for our generation of F-150s and Expeditions. We had so many returns that, despite my boss's opinion, I'd tell customers not to buy our alternators if I saw it was for an F-50.

 

Alright. Thanks guys!

 

Discrete components site- https://www.aspwholesale.com

Replaced brushes and ring on a VW... frugal but good option- maintains the "mass" core assembly of the OEM part.