I have a 2005 Excursion EB with the dreaded 6.0L and I my most recent issue is electrical. Driving home from work I heard what sounded like relays and then everything on the dash, radio and temperature display shut off. The truck kept on running and since I was about 1.5 miles from home I just went for it. When I got home I backed into my spot shut it off and then turned the key to start it back up and everything was fine. I lifted the hood and both batteries were wet on top so I shut it down. I went into the condo and got my multimeter and read the voltage on both batteries. One was 12.58 and the other was 12.48, the wife and I had running to do so I shut the hood and jumped into her 2013 Explorer Limited.
The next day I went to Pep-boys to get the battery checked but they were swamped so I went across the street to Firestone, I thought that I might need batteries and they had the best price on Interstate Batteries. I had to leave it so 2 hours later when they called I was glad to hear the $28.00 battery/electrical check was good. When I went to get it the darn thing wouldn't start, not even a click. The guy at the desk offered to call a tow truck to take it to the local dealer but I refused. I was able to jump it and get it home. The next day I went back at work and one of my fellow employees and I went out and was looking at it and talking about my problem. I disconnected both batteries and put them on a 2 amp charger, once they both were charged I reconnected and started it up. He stayed on the battery while I was cranking and it dropped to the 10.2-9.98 range and then slowly started coming back up, and I mean up. We watched it climb over 15 volts so I took the meter and went directly to the alternator and it went to 18.9 volts so I shut it down. I was able to contact an old friend that worked at Ford and he said that if that much voltage was coming out that the alternator was bad. I went through my records and found out that it was 3 years old and had a lifetime warranty, I took it back to the auto parts store, they hooked it up to their tester and 14.3 volts was all that it would produce, 2 different times. Now I am scatching my head and walking. Anybody have any ideas?

 

I don't know about a 2005 6.0L. I know that the regulator on a 2002 7.3L is on the alternator. I think that the regulator on a 2005 6.0L is in the PCM.

So is it possible that a bench test of your alternator would not show the increased voltage that your PCM is directing the alternator to put out?

I recently had to determine whether or not it was a bad PCM or a bad alternator in my wife's 2000 Dodge Dakota. (The alternator regulator is in the PCM on the Dakota and is therefore part of the "charging system." It was showing a code "1682 Charging system doesn't seem to be working well. Check alternator, etc." I determined that the alternator was bad, replaced it and everything was fine.) But in response to a question on the Dakota-Durango.com forum, I got this answer which you may find interesting regarding "full fielding" the alternator by an inadvertent ground:

"The regulator controls the amount of current to the field circuit in the alternator, basically making the rotating magnet stronger or weaker to maintain the output voltage.

It does this by switching the circuit to the field, very fast, up to 100hz.

The output from the stator is not switched at all and is connected to the battery.

Colors vary between the Durango and Dakota but on a 2000 Dakota, if you ground the green wire on the alternator it will "full field" the alternator and make it produce it's full output.

It's an 18 gauge wire."

Could you have an inadvertent ground in the vehicle which, when your alternator is in the vehicle, is "full fielding" your alternator causing it to produce its full output?
No doubt the wire color and gauge may vary, but the concept might apply to your problem.

So, we can all learn from your experience, please post what you find.

 

According to this diagram, the diesel in 2005 did not have the computer controlled alternator. I looked up the smaller trucks and they did.

Take your meter and make sure you get 12v on the orange/lightblue wire at the alternator. I think that's the feedback wire(voltage info) for the regulator.

 

Thank you Franklin2 for correcting my concern. (Please keep it up. I am now watching and participating in the electrical forum to learn. Just think of me as the guy who asks stupid questions.)

Is there a way that the configuration of this alternator could go "full field" output while in the vehicle but not while on the parts counter bench?

 

I am not sure, but I am thinking if the orange/blue was shorted against some metal, it would blow fusible link E, and the voltage to the orange/blue would go to zero. This may make the regulator demand full output from the alternator. Just a theory.