I purchased the Spal controller seperately and I highly reccommend it even though it is not the cheepest around, but it lets you use the stock temp sensor for the computer and you get to set the temprature for the fan to come on first at 50% and then the upper temp for 100%. The A/C sensor input runs the fan at 100%. I believe you could put a switch in the ignition sens lead to turn the fan off for water crossing.

There is a noticable improvement in power in warm conditions when the OEM fan is engaged a lot.

There has also been about a 12% improvement in fuel economy.