Kathy, I joined St John Ambulance in 1964 as a volunteer - we had EJs and EHs - and then rejoined after National Service in 1968 (HRs). They all had thumping great chrome sirens bolted to the roof, operated by a 2nd dip-switch on the trans tunnel. To get the siren to wail, the driver had to operate the dip-switch: on-off-on-off-on-off. That was OK until you hit the wrong dip-switch under the canopy at the Royal Adelaide Hospital - scared the daylights out of everybody
I think the cops had similar sirens.
Martin