Good news,
Well it turns out that the wires from the footwell lights weren't too hard to trace after all. A pull on the wires underneath the bus led up to a live wire with a fuse holder. The fuse had blown, so with a new bulb fitted and new fuse installed the footwell lights work. Errr, well at least the front passenger one does. The side door footwell light still requires a new 12 volt bulb holder.