Try searching t'internet for g3radfan3speed.pdf, and you should find a two page PDF containing a wiring diagram.
I've not checked it (some wiring diagrams do have errors in them), but it seems ok on the whole...
There is a cool thread on the Corrado forum describing the cooling system, which may be worth a read:
http://the-corrado.net/showthread.php?38925-The-definitive-VR6-cooling-guide