After a serious under dash electrical fire in another vehicle, I prefer separate power sources for fans, stereos, etc. using relays with individual fuses to the accessory(s) and ignition key-on wires for each relay.
http://good-times.webshots.com/photo/2239546800083629245UPRxnN The image is the set-up for my fans that mounts under the dash. A wire directly from the battery to an 80amp fuse, connected to a four post distribution block, 30amp fuse for each line between the block and relays, 30amp fuse from each relay between the relay and accessory.
I have a separate distribution block for all key-on relay wires, which requires only one wire from the ignition to operate all key-on accessory relays.
