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You don't need that big of a switch. I would use a 30 amp relay and an illuminated switch to power the relay. That way, your fan would run from the battery, instead of through the switch.
Use 10 gauge wire from battery to relay and from relay to fan.
the fan switch is put on the ground and all it does is ground it out so the fan works.All you need is a cheap toggle switch wired to both relays not the a/c relay,to the switch and then ground it out.Go to Mid america and they have instructions on what wire to hook up to.You justr got to put a hole thru the firewall.