I have a 98 expedition EB 5.4 The Battery light comes on and volt gauge goes down steadily. I've had the alt. tested 3x and it's fine, replaced the belt and checked the battery. I was told to test the 3 wire connector on the alternator. I checked the two outside wires, the one on the pass. side has power with key on. The one on the Drivers side (orange) didn't. I traced it to a fuse holder in the main fuse on the firewall. This wire is in the loom with the main power lead coming off the alt. that runs to the main fuse. In that fuse holder is a 20a fuse that was blown. I replaced it and it ran about 14 miles before the fuse blew again. Anyone with a suggestion? The fuse is fed by the terminal that the main lead from the alternator attaches to.
Thanks!!!
The fuse in question is below and right of the bottom disconnect, you can see the orange part of the fuse in the picture.

 

Either the Fuse holder, Orange wire with a blue stripe leaving the fuse holder is shorting to ground or you have a bad alternator regulator. This is the "A" wire to the regulator.
My guess is you need to replace the alternator or its regulator.
The regulator is replaceable on your truck.
The regulator is in mounted in the alternator.

By the way it is called a Generator and not a alternator on your truck by Ford.
Ford does not use the term Alternator.

So here is how Ford says to do it.
Removal

1. Remove the generator (GEN) (10346); refer to Generator in this section.

2. Remove the (A) generator brush and terminal holder and the (B) voltage regulator assembly.
1 Remove the screws.
2 Remove the (A) generator brush and terminal holder and (B) voltage regulator assembly.


Installation
1. Install the (A) generator brush and terminal holder and (B) voltage regulator assembly.
1 Depress the (C) brushes and insert a (D) wire to hold brushes during installation.
2 Install the (A) generator brush and terminal holder and (B) voltage regulator assembly.
3 Install the screws and remove the (D) wire.

2. Install the generator; refer to the generator in this section.

Ref. Image:
http://i54.photobucket.com/albums/g9...XGenerator.jpg

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Thanks for the intel Subford.
I replaced the fuse holder and have since driven 40 miles with no problem. I did notice a small amount of corrosion in the fuse holder. I will monitor it closely and I'm prepared to purchase a new alternator. I tried the brushes etc. on another one and ended up purchasing an alternator (generator) a few weeks later.
More news as it happens.