Grady, Urban's got it.
It's completely variable. When I reach 187*F (the temp threshold I set it to for a 180 Mr G t-stat), it starts ramping up (like a jet engine spooling up). It simply keeps ramping up more and more to keep the car at 187 (it's designed to run +/- 1.5*F of the temp setting, as I recall from Brian's tech specs). It ramps down just the same way.
Because it's variable, as Urban said, you connect it up to high speed fan terminal only because that allows the fan to run at it's full potential if needed. But because it soft starts, there's no shock to the electrical system (start up fan draw, etc). and it keeps engine temps stable.
It also turns on the fan to 50% with AC (when you are below 187*F - it obviously ramps up more once you reach 187*F). And there's an U/D jumper for you guys with pulleys - it runs the fan at 10% at all times to help compensate for the UD's.
For anyone in a hot climate, it's a great thing (that is, for the non-tuning crowd who cant adjust the factory thresholds). But even with being able to do so, the variable nature of the controller blows away antiquated relays and on/off switches.
Y'all know I'm a poor SOB, and that controller was worth every penny! And Brian's a super busy guy (he's the owner - a one man show), but his tech advice is second to none - he will take care of anyone who has issues (and there are some real stupid people out there who ask him some real stupid questions). Top notch product.
The FK-35 is what he recommends for the SN95 fan. Get the optional LED that he offers - you can see how hard the fan is working. I got the rheostat too - I can dial in the exact temp that the controller wants to keep the car at - I like to fiddle with things like that. You can do the same thing with jumpers on the controller itself, but the rheostat allows one to make adjustments from the cockpit.