There are variations in the wiring loom so I don't think you'll ever get a wiring diagram that you can rely on absolutely, but Steve Heath's book the Griffith / Chimaera has a wiring diagram which is probably as good as any. Available from the TVRCC office.
You can't even rely on the layout of the fuses and relays found in the owners manual. (from personal experience)
The wiring diagram in the bible is about the best complete guide there is. It's not too difficult to check what's there - TVRs are quite simple cars after all.