Be careful getting it to thermatically switch as well. My autoelec originally did that, and when the fan switched on from the thermo switch, it also switched the A/C on - but the ECU didn't know, so the engine would stall under the load.
Just rewire so that it comes on when the A/C clutch engages, and leave it at that. As I said, the standard engine fan can draw more than enough air to keep everything cool. I was driving in Adelaide once - 40 deg, black car, A/C running full blast, and the temp gauge never budged.