[dpjmw]

Do I need to do anything fancy like relays or whatever? I am planning on just making it come on when the ignition comes on with a hot wire from the key. Its hot in texas, so I figured it would not hurt to run it all the time. Any thoughts from your experience would be greatly appreciated.

[EBlack36]

Run it through a relay, they pull a lot of current at startup and run it through a switch of some type either a manual of a temp activated type. All the switch will do is to turn the relay on and off.

[dpjmw]

What is the purpose (function) of the relay?

[foestauf]

Yes. You definatly need a relay. Most fans draw 20amps, that will fry your wiring box, and or switch.
Just find a spot on your fuse panel that is hot only when the switch is on, and wire that to the trigger terminel on your noid.
I would also recommend instead of doing that. (But the info is there if you really wanna do that)
I would recommend hooking up a temperature probe, I got one from Autozone for like 20 bucks. Wire that ALWAYS hot, directly to the battery with a fuse of course. So wire the PROBE always hot, then wire the probe to the trigger on the relay. This always your fans to function on and off (The probe is adjustable) like normal. But the part I love the most about it is that after you turn off your car the water just sits, so the temperature will rise. This setup will allow your fans to run for 1-2 minutes (depending how low you set the temperature) after you have already turned off your vehicle.
I did this setup on an IROC-Z that I own, I am really liking the setup. If you get a probe that taps into your heads you could also wire that to an electronical water pump, wich would allow your car to warm up faster and cool off faster. ESP great for hwen you shut off your car, go into a convience store for 5 mintues and start it up again.

[Pony]

Although it's a little pricey @ $60.00 Painless sells a complete set up that runs the fan automatically. It contains the relay, temp probe (install in head or block), circuit breaker and all necessary associated wiring. Their are two versions: (1) 220* on -- 185* off and (2) 185* on -- 170* off. Running the fan all the time puts an unnecessary load on the battery and fan alike also there's always the chance that you forget to turn the fan on and hurt the engine before you notice. The automatic set up takes care of everything and lets you enjoy your ride.

[dpjmw]

Okay, I'm convinced. I will probably opt for the painless setup. BUT, can anyone tell me what the purpose or function of the relay is? I don't know what it does, and that bothers me. And what about resistors? What do they do?

[Pony]

You don't want to run a lot of amps (power) thru your switches and also the longer your power wires are the more power drop you have. By mounting the relay close to the object your powering and running your heavy gage power wires to it, you supply it with more power and can trip the circuit with a much smaller wire form a sensor or switch.

[horvath]

The relay takes the power-jolt off of the switch and handles it INSTEAD of the switch. It also creates a more direct power source -- instead of the power wire running all the way to the switch and then back out to the fan, the power wire goes directly to the relay and the relay sends it directly to the fan.

When an electric fan kicks in, it (initially) draws a whole lot more than 20 or 30 amps and a relay handles that much better than a switch does.

When a fan turns on and off a LOT, the contacts will wear sooner ... to avoid that, I use TWO relays on my 16" fan:
See Here

Alan
54 Chevy Pickup