David, take the protective cover off, from top of the fan inside the hood (there are also two screws under the weather strip). See if it is running on the off position. If it is, then what Geoff was saying is correct and the slide on the off position is really the first speed of the fan. Now, you can also take the wires off of the fan and at least you stop it from running, but make sure you cover the ends with electrical tape, since it is obviously getting power to it all the time, until you or your mechanic can find the problem.