Here's what I have:
this is the column end: (a little polish splattered)
http://homepage.ntlworld.com/chedzoy/cobra/col.JPG
this is the boss.
http://homepage.ntlworld.com/chedzoy/cobra/boss.JPG
Clearly not a pair. I hope the sierra specific boss fits this column and allows for a switched live to the horn, the boss I have only allows for a switched earth.
Maybe we have the same problem?
cheers
Graham