enough amps
I just purchased a Lincoln Mark Viii fan for my ride. I won't be installing my till next spring but I have been doing a lot of research and the one thing I keep reading is that you need at least a 130amp alternator. I see you already have that issue covered along with the 70 amp relay. These are the only two requirements that everyone definately agrees on. Also how you activate the fan, I like your idea. I was considering doing mine the same way. Two relays, two switches,plain and simple. No electronic controllers to go bad. Just keep your mind on what your doing and keep your eyes on the temp guage.