This is a clutch fan. the twin fan setup is to replace this, and the AC fan.
That is why they are wired separately and only 1 plug in the factory harness (as the clutch fan is mechanical).
you can wire them together and have them run full time with an ACC on 12V source, or you can wire 1 to an ACC source and the other to the factory AC fan plug. The choice is yours. the Factory Clutch fan will no longer be needed and can be removed.