I've seen the posts about putting a switch in the cabin to manually turn on the radiator fans, but how do I rig the system so the fans stay on (when the coolant is hot) after I turn off the car? Hondas, Volkswagens, and others behave this way.

 

There are just too many things the ECU considers in controlling the fans. Best to leave it alone.

 

you can run a relay controlling it with a timer that would activate once the key is in the off position.

but why does this bother you? are you concered with cool-down between track runs or something?