Post #9 has a diagram and pictures of the mega fuses, and some well written suggestions.

 

Take a look at the picture in post #9 for the mega fuses for more than 2 seconds :



Notice the Battery in the picture on the left ?

While you are at it, read the text that describes the location of the fuses :
Pay attention to the word cover in that location description. All of this is in the owners manual.

On to the wire, did you check the wiring for cracks and the connectors to make sure they are in good repair ?

You need to focus on diagnoses of one problem at a time, bringing up horn issues right now is not top of the list of things to work on.

My opinion, you have what jbrew talked about in the URL in post #9 above as to why the battery is not being charged; but that will take some diagnosing work to confirm or deny.

If you think it was some person on some forum that agreed with your buddy ( that changed your alternator ) you will need to stop asking here for the URL and find it yourself.
I only have suggested diagnostic steps as to why your battery is not charging.