yea you can straight wire a switch but not recomended, for instance if you forget to turn it on one day and it overheats you could be in some ish, all you would have to do is pull a hot wire into a 2 position switch and run it to the feed wire on the fan, you would have to find the hot wire on the fans 1st before wiring it up, also would need to ground switch if not self grounding. and your sure it runs constantly when car has been off for a while? it will cycle on to make sure engine and or coolent cools down even after engine is off. but shouldn't be doing so hours after being shut off, good luck