In a LOT of cases, there is a manual switch wired in - - I have one on my car! Could it be that the previous owner had a manual switch he forgot to tell you about? If this switch has the fan turned on, then the fan would run as long as the ignition is on. I also know of one car that the owner had an overheating problem that he could not find the answer to, so he directly wired the fan to run constantly (without a switch)!!

If there hasn't been any rewiring in this circuit, then I would think you have a faulty Fan Switch on the engine (It turns the fan on/off when the temp reaches a certain point).

Check out our new technical info and tips section under fan relay and temp sensors. Both responses by Ed Parks could relate to your problem (even though the questions asked of him do not).

Hope this helps

G