Rear Defogger Switch
WARNING: This page is about a different car, the 1997 Ford Expedition. However, it is still accessible from the selected car via links, so may be relevant.
Remove rear defogger switch. Measure resistance between Dark Blue wire terminal and Black wire terminal on switch. Resistance should be greater than 10 k/ohms. Press and hold rear defogger switch button. Measure resistance again between Dark Blue wire terminal and Black wire terminal on switch. Resistance should be less than 5 ohms. Replace switch if measurements are not as specified.