I have a 2005 S2R Dark the horn switch no longer functions. Do all Ducatis left switches have the same male / female connection on the wiring harness?
The connector isn't the same for all the left controls as it changed over the years and with different functionality. (there are molex connectors and various 4/5/6 pair and twin set of connectors ala 696 and Hypermotard) Also not all left levers have the choke / enrichner level on them either.
Get out your multimeter and test the functionality of the horn switch wiring itself before going further. It's a pretty simple switch in there and takes @4 minutes to fully disassemble if you do need to do repair work on it. Essentially just two springs and a simple contact plate.
I'd test the horn to see if it is actually working itself first -- just run some 12v+/ground wires to it and connect for a second.