Electric cooling fans and manual toggle switches are a recipie for disaster unless there's also an automatic shutoff in the circuit designed to stop the fan when the ignition switch is turned off. Otherwise it's only going to be a matter of time until you forget to switch the thing off and run the battery down. A simple automatic on/off circuit that incorporates a thermal switch set to a predetermined coolant temperature is a lot wiser choice.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!