I saw a truck at a event yesterday and he was claiming with all 4 fans on he was moving over 9k cfm. 2 where large 10 inch fans set up off a relay and 2 smaller 8 inch fans with a manual control switch in the cab.
Yes, there is a wire you can hook up to manually turn them on.......I have the Flex-A-Lite fan setup sitting in my shop...I changed them because I needed more room in front of the engine.
Yes....like Ivan said...there is a VSC controller where you can set the fans to come on at any temp or you can hook a wire up to the controller to manually turn them on with a switch or manually turn them off with a switch.