Matt,
They were never (as far as I know) fitted to Ferrets in service. You can retro fit one, as some owners have, by connecting a 24volt beacon to the auxilary power connector on the distribution box. This is the small 2 pin plug near to the inter-start connector. I have driven thousands of miles in mine without a beacon, technically driving at motorway speeds in a Ferret with the beacon going is illegal anyway.
Chris