Ok, this might be long, but bare with me because I am trying to cover my entire situation so I can get the most direct feed back!

Car Info;
2004 Ford Expedition XLT 5.4L SOHC 8CYL 4x4
4x4 Modes; 2H, A4WD, 4H, 4L

I purchased from a private party the first week of Feb, Mileage @ 104,000

ok here goes...

when I bought the car the 4WD system was working perfectly, all selections were working as designed, no issues. THEN...my wife had left the radio on after she got out one night( its an after market radio and the person I bought it from had wired it himself, apparently wiring it either to an "always hot" wire or by passing the ACC wire or both, not really sure there) anyways...so she left the radio on which had killed the battery, no problem, so I went to jump it and had an old sh--ty pair of cables that eventually completely broke from the gator clamps which then rendered them USLESS. So I had to think of another way to get the truck started WITHOUT cables. I then thought to just put the battery from my car into the truck just to start it and leave it running while I switched the old battery back in to get the alternator to charge it back up, simple enough, should be back on the road in no time right?! wrong! I happen to be on the phone while putting in the car battery and didn't notice I was putting the battery in backwards, uh-oh! Still not aware of what I did, I connected the battery cables and immediately the connection gave a huge spark, but by the time I was able to process this, both connections where already on the battery and the fusible link started frying and smoking like crazy. So I backed away instinctively thinking that the battery might explode and waited a few minutes (approx. 2-5 min), then I pulled the pos connection off the battery and let it sit before I assessed the damage. So when it was all said and done I had destroyed the alternator wiring harness and burnt out the alternator (not sure if it was just on its way out anyways, looked a little rough to begin with). So I order a new alternator, bran new not used or reman., and a new wiring harness. The order comes in and I do a quick swap and the truck is back up and running again. Everything seems fine until I go to turn on the 4WD system and nothing happens. The first thing I checked was the fuses in the fuse box located in the kick panel. I checked every single fuse and found three fuses blown, they are as follows;

Fuse Location 4 - DVD player, Rear seat audio controls, CDDJ
Fuse Location 20 - 4x4 Module
Fuse Location 24 - All interior lights, Battery saver relay coil, battery saver relay power

So...I changed all the fuses and went back to the drivers seat and started the truck and the 4WD system still did nothing. So again, I checked all the fuses and everything was fine!.....huh!?...starting to get confused at this point. I took my volt meter and tested Fuse #20 micro fuse on both sides and I am getting normal voltage.

So here is the current issue;

When turning the 4WD control switch to any of the options I get nothing, not lights on the instrument panel for 4H or 4L, no sounds of it engaging, its like the system is completely dead.

If someone could help me diagnose the problem it would be GREAT!! I am very mechanically inclined (please excuse the battery situation, I know only a retard would do that, but don't get a bad impression because of that one, I admit my horrible mistake )

THANKS!!

 

What about fuse #115 (30-amp) which powers the 4WD shift motor and front clutch, is that one good or bad?
Check fuse #11 also.

 

Yea, I was told to check fuse 11, fuse 20, and fuse 115, non of them are blown, how ever I haven't checked them all with the voltmeter, I only checked fuse 11, I will check them when I get home from work and post the findings

 

It was a fuse, fuse number 20, even though it looked ok it was blown, tested both sides with voltmeter and only one side was getting voltage, switched it out and BAM! 4WD was working again! Thank God it was a simple problem and not something more complex and expensive. Thank you for your reply and interest alloro!!

 

No problem, that why we're here!