My truck is sitting at 11.95 volts - too low. Battery is about a year old.

At highway speed, we often see the headlights get brighter for a minute or two, and then dim a bit.

Alternator issue, or battery?

 

Have them both tested, only way to know for sure.

 

What year/model/engine?
First as Kozal01 said have the battery and alternator tested but in the meantime you could help us by checking a few things and reporting back.
What's the battery voltage when the vehicle is running? Headlights off then headlights on.
Have you cleaned the battery terminals and connectors? Even if they look good, clean them to be sure.
Alternator connectors properly in place, fully seated or properly bolted (tight)?
Any evidence like the belt is slipping, squealing?
Let us know what you find

 

I'm going with the most common problem... alternator. being that the battery is only a year old and the fact that the headlights are going bright to dim tells me you have a voltage problem.. that is exactly what goes out in our year alternator's ... the voltage regulator. buy a motorcraft re-man.

 

The alternator's only about five years old too....can I swap out the voltage regulator on it, do you think?

 

good question... maybe, you would have to take it apart... and find the correct regulator... most likely you bought a cheap re-man that only lasted 5 years.

 

did you go have the alt (and battery) tested? That should have included test of regulator.

If if you don’t change your own alternator (and pay labor for it), get best alt you can (ala tech rep suggestion) and hope it last as long as possible. These typically won’t have a lifetime warranty. However, if You can swap them yourself and it’s for a vehicle that you plan to keep a long time and is easy to swap, then I like to get the one with “lifetime warranty” at a major retailer. That way you are always covered for free excange, and can pick up in most any decent size town. They even usually have few loaner tool to do in parking lot if needed.

 

5 years old? Was this a Motorcraft or other brand? New or rebuilt? Some posts here that talk about how finicky these trucks are with third party parts, especially rebuilt ones.

 

It's a motorcraft alternator, and they only sell the rebuilt. It certainly wasn't cheap - way overpriced for a rebuild, I thought.

I'm in Canada, so there are no places to do a 'free' test....

It's rained for days, but I'll try and get out there soon to check the voltages...

 

Max,

I did a search and it looks like Canadian Tire will test your battery for free however you may have to hand it to them (removed from truck). I'd give them a call and see what they say and while your at it, ask if they know of any other suppliers that test batteries for free. I have no idea how far away your nearest Canadian Tire store is to your location. Good luck.