You have 1 relay for each fan, right? This makes the load much more reasonable and gives redundancy in the system (you only lose 1 fan, not both). The best relays are usually factory ones and not something from Autozone. Bad crimps on the terminals take out as many relays as their own contacts failing do. You want factory crimps or soldered crimps, but avoid aftermarket relay sockets unless it is a well-proven brand.I burned up two relays so far with my windstar fans (over about 4 years).
For people wanting to have only manual control of electric radiator fans, I usually recommend using a mechanical fan....