I'd think 12 is okay from the relay to the switch. but but from the battery to the relay and to the fan, I would run 10.
I have 2 small fans on my blazer and thought it would be good to run the power through the IGN wire in the fuse box so they would shut off when I keyed off. The fans ended up producing so much juice that when I'd shut the key off, the fans would keep the engine running.

 

You can also run a small wire from pin 87 to 86 and use a switched ground on pin 85 to control the relay. Sometimes that is easier.

 

so run from my battery to 87, and from battery to inline fuse to switch, and from switch to 86, and from 30 to fan + and 85 to a ground???

 

Battery to fuse to pin 87 (use at least 10awg) make sure fuse is as close to battery as possible.
Fused/switched source to pin 86
Ground to pin 85
Fans to pin 30 (use at least 10awg)

 

thanks, ill wire that up in the morning

 

I would take pin 86 & 30 and go to the battery.

85 to the switch used to activate the fan, the other side of the switch would go straight to ground.

87 to the power wire to the fan

When 85 sees a ground it will send 12 volts through pin 87 to power your fan.

Derek

 

You want to run at least 10ga wire on the circuit powering the fans, since that's where the major load is and where the most current will be. Make sure to fuse that line with the appropriate size fuse. The control side (switch, pins 85 & 86) can use the 12 ga that you already have...you probably could even use thinner wire if that's all you have since that is a low current circuit.

 

Right, just to help you understand when you wire this thing, relays are used to keep the big wires that carry a lot of current as short as possible and to limit the number of wires you have to run into the cab. With a relay there should be only one small gauge wire coming through the cab. The power circuit should be the larger gauge wires and signal wires can be very small if you want. Make sure you get a relay that is rated at a high enough amperage for the fans.

 

so run 86 & 30 to the hott on the battery ???

 

its a 30 amp relay and i have 30 amp inline fuses which is enough right?