Trying to figure out how to obtain the Fire-horn I got from backing kickstarter. I click on it in GOG, and it appears to load, but I am not finding it. Anyone have any idea?

Click the Fire Horm DLC item and download (as you have done)

Then go to the folder containing BT4 - you can quickly go there in galaxy in the game tab, More -> Manage Installation ->Show Folder

In the folder, find a PDF called Firehorn Bonus Card.pdf

In that PDF is a "passphrase" and instructions how to add the item to the game.

Note the Instructions are partially wrong, pressing "enter" does nothing, you need to click the button at the bottom of the screen that says "apply changes" (It appears once you enter the code) - EDIT: oh, and your code will most likely be in lower case in the PDF but you will have to enter it in upper case as you won't be able to change case. Doesn't make any difference.

If the code worked, the area where you typed it changes to a smily :)

The Horn can be found in the old Adventurer Guild, upstairs, on the walll