The OEM relay has 2 separate inputs (low and high), which in my case I have the low speed routed through the FITech unit to control it, and the high speed wire I have routed to the OE factory fog light switch for "manual" control. Outside of the FiTech control component (which I was doing anyway, the fan control is a byproduct of the system) I figure I have about $9 total in my relay (2 relays JY pulled $7, a bit of wiring as part of an AAW harness). The FiTech also provides the sensor (required by the system) that provides adjustable control for on and off temps. I did buy a new factory fog light switch as mine was pretty beat up, cost me another $26.
Again I have no real world experience yet, and some of the $80-150 fan controllers look cool, with some wide ranging results (love it, hate it). I'm not suggesting that my route is the best route to take, only that OEM engineers addressed the voltage and relay concerns for the dual fans where they MUST survive a 5 year warranty period and say 10k start cycles? If it works for them I can't see how even a daily driven classic could not see the same positive results.
If you wanted to go all new, the relay is about $35 from Rockauto but you will likely have to go source the connectors in the JY (my original plan until I found lots of relays and connectors waiting for me). The fan I used was new however from RA. Hopefully firing it all up around April 1st.
1966 GT Coupe
Not much left original
Trying to do things once
MMI CO / Panhard ~ JRI / Penske ~ Astro A5 ~ FiTech ~ MGW ~ AAW