There's not much you can do in a situation such as this except explain as diplomatically as possible that the wiring has deteriorated due to age and is in need of replacement.
I can't find a pic of a Cryselco light, but by "single arm" do you mean something like this Mazda fitting?
Ad taken from a 1964 magazine.[This message has been edited by pauluk (edited 08-17-2005).]