The sirens on many of these appliances were mounted in the engine compartment and operated off the fan belt with a spring-loaded cable running back inside the left front floor and attached to an accelerator-type pedal. When the station officer stood down on the pedal the cable pulled a shaft attached to the rear of the siren rotor onto the moving fan belt. The result was a fairly effective siren. Some set-ups had the cable running back to the dashboard with a handle mounted for the officer to pull. Perhaps David you may have a chance to photograph one of these, thanks?
Added by Pav on 13 December 2011.