[TR] Fiamm/Hella air horns on TR4-TR6

[Chris Kantarjiev]

I've had a couple of the "all in one" Fiamm air horns - the compact
ones that mount the horns directly to the compressor body. 

They're really not very good. They draw a lot of current (10A or more) and
the point at which the horns mate to the compressor tends to start
leaking after a year or so. 

I use the Hella Supertone horns now, which can be mounted to the
original horn brackets and are really quite loud.