Outer Limits 4x4 Board

just got a set of thermos out of an AU andd want to wire them up. ive done a little bit of wiring on the truck but its pretty dodge. and being the engines cooling i want to do it right. i want to have each fan running of its own switch but not sure about relays and what size fuse or even what power source to run it from. any ideas?????

So you don't want them automated- and just want to be able to switch them manually from the cabin?

You'll need to run relays to handle the current (one for each fan) and fuse them both - probably a 15 -> 20 Amp fuse wired directly to the battery. Use heavy cable to reduce voltage drops to the fans, even 0.5v drop will make a significant difference to the fan speed.

Put the relays in the engine bay (somewhere relatively protected from water) and run a wire into the cabin from each relay's coil (earth the other side of the coil in the engine bay.) Find a 12V source under the dash that's live with the ignition on and wire that to the switch and join the relay coil wire to the other terminal on the switch.

If you want them automated simply buy a thermo switch from any autoparts store and plumb it into the water jacket. Then run the relay coil wires to the thermo switch and they'll come on automatically when the switch is activated by the water temp rising.