I just wanted to know what others did and what is recommended. I know in mavdog71's writeup he didn't use a temp sensor and just wired it to key-on. In the write up on FORDMUSCLE they used a fan controller and a relay. I guess the point of doing this is so that they fan isn't on unnecessarily.
They generally work the best with a thermally controlled switch and relays. My Black Magic has a built in temperature sensor that physically touches the radiator and reads the water temp that way. It also has an adjustable switch the you can set between about 180 to 240 degrees. Some basic info: http://www.aaroncake.net/rx-7/efaninstall.htm
Seems that by NOT having the switch you would need the relay. Just for the simple fact of needing to switch the fan off and on I would think it needs the relay. Is yours on a thermal switch? If so, the article states using the relay is recommended.
In a basic system, yes you need the relay to take the pressure off the thermostat and/or manual switch running to the cabin. The Black Magic fan control unit has all this built in, saving me additional wiring. Yes, the thermal switch/relay control is built right into the shroud and is completely automatic. I simply have a 10" 10 gauge wire running to my auxiliary fuse panel mounted on the passenger shock tower. All the switching on and off is completely handled by the control box built into the shroud. Similar, but newer model: http://www.flex-a-lite.com/auto/html/160_black_magic_s-blade.html If you are installing a basic fan without any electronics, you would need a thermostat installed. . You would run the thermostat wires to the relay to take the load off of it. I didn't have to do this with the Black Magic because it's already built into the unit (see the little "box" at the top of the photo in the link.
Ok, I see the boo-boo. I should have said...."it didn't need a secondary relay." The relay function is in the control box built into the shroud.
You need a relay regardless. Big gauge wire coming from the battery to a relay, then from the relay to the fan. A small wire coming from a power source to the relay. Now if you want a tempature switch all you have to do is put a smaller gauge wire from a power source to the temp controller. From the temp controller you'd wire that power out to the power in on the relay. This way you fan gets adequate power thru the big wire underneath the hood, and you don't have to run that huge wire inside your car.
