I was never able to find a wiring diagram online. I went ahead and bought the service manual. I'd offer to e-mail specific pages, but the UK version likely has too many differences to be useful.
Honda sells paperback service manuals in North America through Helm at helminc.com; not sure about the UK. One is called Electrical Troubleshooting. There is also a bootlegged CD-ROM service manual often being sold on eBay.