Yeah a flakey alternator probably or lord help you a loose connection somewhere. Alternators will start to get intermittant when the brushes or regulator are on their way out. A low voltage output will cause the light to flicker. An output that is jumping around will also cause the light to flicker.
What do you mean the alternator looks full?? Did you measure voltage at the battery? Was it something like 14volts to maybe 18? What is full?
I have never had an American made alternator go out on me so I never had to rebuild one except in class. Could be luck, or we know how to build them bullet proof. Had plenty of practice rebuilding Japanese alternators, jeez blow out on schedule it seems.
I DO NOT KNOW if modern alternators have brushes. So it will be up to you to findout or for someone who does know to step in.
If it is brushes, it should be a simple job to replace them, and I would replace the bearings and touch up the commutator while I was at it. For a quick and dirty commutator cleanup, just wrap a piece of say 400 or finer sand paper around it and twist till it is clean.
I more suspect that a diode in the alternator has been toasted. Alternators have full wave bridge rectifiers, which are basically 4 diodes that convert AC to DC. It is common to have one burn out, especially if you have recently had battery problems. The alternator will still work with three diodes, just not at full capacity, plus you might get some "hum" type interference in your radio. It will change pitch with engine speed.
I can't say if the alternators are servicable. these days people just yank them and get a rebuilt. It isn't like my old '56 F-100, where you actually serviced the generator.
came on a month ago, had batts tested replaced a bad one, now it flickers again, not very often, just enough to make you think.
checked the alternator and it looked full...
any ideas ?
With the parallel dual battery setup in these trucks, when one battery starts to go, you must replace both batteries at the same time. If you do not the old battery will quickly shorten the life of the new battery.
Thanks for the info Redford! I sometimes dont ask questions for fear of getting bashed to death by the hardcore diesel guys. I'm still getting used to all the extra stuff the 04 has. My 99 was a v-10 and didnt have all the lights and such. The 6.0 is beast thats sure, thanks again.