Then you really have no way of knowing what is wrong.

When you accelerate, the truck uses more power (e.g. FICM) and less when you are at idle.


Do a proper alternator test --- eg measure voltages at the battery sense and light wires... and also do proper measure of output via clamp on ammeter and volt meter.

 

you have a bad alt. it took me 3 to get a good one, exact symptoms youre having i was having.

 

That is possible, it is also possible that it is a bad pigtail.

 

Went out & tried to start this morning & it barely turned over so something drianed the batteries overnight. I haven't had time to get the alternator off, it will probably be tomorrow before that happens.

 

If the alternator bench test fine, your problem is likely elsewhere.

 

A bad diode in the alternator can drain the batteries over night. I think this may be telling you something.

 

Ostensibly, this is a brand new alternator...

 

Read the other replies of people that have gotten bad rebuilt alternators. Some that took 3 or 4 to get a good one. Rebuilt means what the rebuilder thinks is bad gets replaced, nothing else. Diodes can be self healing and show up good after cooling down and after heating up fail again.

 

Been There - Done That with respect to bad alternator rebuilds. Furthermore, seldom (if ever) is a rebuild tested in under-hood conditions, like vibration and 200 degree air blowing across it. I had nothing but bad luck with rebuilds, but have had great luck with the Advance Auto alternator, because it was NEW, not reman. Hence all new parts.

EDIT: It was a little more expensive, but worth it, as it also has a lifetime warranty. Not saying I have not seen the problem with the pigtail as well. BUT, with something killing the battery, and the only thing that has changed is the alternator, well.......

 

i think the only thing that drained your batts was the fact your alt wasnt charging them when it would run.it could very well be a pigtail issue too.

 

Ok guys is the pigtail a dealer item only? I will probably order one so I can keep eliminating issues. Thanks for all the input.

 

It is available from aftermarkets, but if none is nearby, pony up to Ford.

 

And fully charge those batteries so you don't take out the FICM.

 

Quality rebuilders test the components at operating temperature and conditions.

But if you buy a "no name" rebuilder --- you are on your own.


I went with a custom rebuilder --- one that I can march back to and complain if the thing failed.

 

Did you ever come up with a fix for this? I'm having the same issue.