By the way, I have one of these as well but unfortunately the person that packed it up somewhere, either in the factory or in some military stock facility, had wrapped it up to tightly so both of the cable grommets for the horns and one of the Hella switches had broke when I unpacked the siren-light.
The cable grommets are of an old type with different thread than used today and the Hella switch is also out of production.
I have replaced the switch with one made by RS that look quite close to the Hella.
Of some reason Hella use the same part number as on this switch for a completely different design today.
I got a replacement from the selling company but of the contemporary type that do not fit.
Sooner or later I will find the right parts.
Michael