Window switches are diagnosed by process of elimination, from most likely, to least likely. The fuses are checked first, then the power at the switch, then power coming from the switch. If the power going to the switch is present, but the power coming from the switch was not present when pressing the button, the switch must be replaced. If the switch sends power, but the
window will not go down, the power at the window motor would be checked, to find if the window motor is functional.