Uninstalling:
I was scared when my horn was not working since I have heard horror story about the pain it is to change it. After looking I found out on my 2007 Mini Cooper S (I would assume that all 2nd Gens are this way 2007-2014). All that you have to do is remove the headlight. Then you can easily take out the horn.
The culprit of the problem:
A couple things were wrong with my horn. First, I had a blown fuse (f44). I picked one up from my local AutoZone. After installing it it would click but not actually blow the horn. After this i took out the horn. The problem is that the horn has a "fluted" end for lack of a better term. That was facing straight up. Which acted like a funnel for water to get into the metal base of the horn (I poured out about 3 ounces of water from my horn). A side not is. I tested the connector of the horn and got my 12 volts. If you are not getting voltage when pressing the horn you have bigger problems.
I hoped this helped someone.