Switching the relay ground is best (safe) because if you pinch the wire somehow and short it to ground...there is no fire. Your fan just stays on.
These links should have the info you need:
Pelican Link 1
Pelican Link 2
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74 Targa 3.0, 89 Carrera, 04 Cayenne Turbo
http://www.pelicanparts.com/gallery/fintstone/
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