[rsk289]

The original street leafspring COB cars' horns were activated by the press button on the back of the VW-style indicator switch. The car in the photo has had a few changes over the years, by the looks of things, including later gauges and switch additions. The knob on the far right is, I think, the fresh air push knob, and the large black knob, which is not an original style, is where I would expect the push switch for the screenwasher to be. As the car seems to have a plexi aeroscreen type fitting, screenwashers might not be fitted, unless for driver-cooling duties. I suspect it's been rewired so that switch could work the horns as the steering wheel centre looks like the usual aftermarket plastic blanking cap. Unfortunately the indicator arm is not visible.
I'm not sure what the 'FIA' coil spring cars had.