Power source w/ignition on?

I could use that to trigger a relay.

Also where do I hook up to the a/c so that I can turn the rad fan on with the a/c switch? I have looked everywhere, checked power from anything a/c and nothing.Trying to setup the flex-a-lite thermostat to come on with a/c and ignition only, right now its hooked up to battery only so its on even with the car off.