On the electric fan it tells you to hook one wire to the battery( high amp) and one wire to a low amp source...now couldn't I just hook them both to the battery? I dont see why not
Hissin's right - if you hook the relay's 'trigger' wire directly to the battery's hot terminal, the fan will run all the time. Well, at least it will run til the battery's dead.
Here's the ONLY way to control your electric fan -- www.dccontrol.com.
I hate to argue with Mike cause he seems to know everything, practically, but here goes. The dc control he listed is the best way to go, I plan on getting one of these too. Its not the only way though. I know some guys running bosch 75 amp relays and they have them wired to a key on source on the low amp side(trigger wire). The fan runs all the time the engine is on and the stat sets the temp.
I dont recommend this, but mine is wired to a 30 amp relay and switch. I watch the temp guage and turn it on when needed. Usually on all the time in the city and off on the hwy. I am still running my taurus fan on low speed, been through 2 Florida summers like that with the AC on in traffic. I have forgotten to turn it on at long red lights and seen 210* on the guage. Thats why you shouldnt do it. I also have a 3 core radiator. Then again, if the control unit were to fail and you are not watching the guage, same thing could happen. I am happy to report my 75 amp 2G alt is still alive and well. I am still drawing under 11 amps with the fan on low and everything hot. Just luck I guess. Dont try this without meters to check it, you will burn your car to the ground.