I was wondering where i could find a power source under the hood that goes on with the ignition. It is a 2006 f-150. I have heard of people going directly to the battery seeing as how the tranny cooler fan shouldn't run all that much anyway, and if it ran for a little while after the truck shut off it wouldn't be a problem.

Also what size fuse would you use to fuse a 8" fan?

Thank you,
Nick

 

The diameter of the fan has NO relation to the fuse - look at the rated draw of the motor in Amps, then use a fuse ~130% of that. The fan power should go directly to the battery (thru the fuse), but the relay that controls the fan can be triggered off almost anything. I'd go with the EEC PWR circuit, which is a plain red wire going to almost every sensor & actuator under the hood.