Rear defrost

It sounds to me like your switch is probably bad. Trust me, these things happen with aging Fords. I believe the same defrost switch was used for Crown Victoria's and a few other Fords so the the part should not be hard to find. You should be able to get the part at an auto part store for relatively cheap. It can also be a poor connection. Does it do it even when you don't press the button? Does it just turn on by itself?

Yes it goes off and on and I don't even touch anything.

What is involved to get at the switch?

Hi Larry! Okay, so... I was actually mistaken about the switch being shared with the crown Victoria (probably a good thing because thaat would be much more complicated) The switch is located to the left or the radio, right? So if you have the proper tool to remove the radio (You can actually use a wire coat hanger), it is very easy to take out! Should just be a plug and a few screws.

Ford changed the interior of the Taurus so much that I really don't know what model/layout it is. If it is located to the left of the steering wheel or away from the radio - let me know. It is also a fire hazard! I would recommend that you find the fuse and pull it.

It is to the right below the radio. This car has auto temp control and all of the other bells and whistles. I guess that I can use a coat hanger to pull pull the panel out and then get to the switch. I would guess the switch is a dealer item but would this solve the problem?

No guarantees that it would fix the problem because it could be other issues also -- The witch is the most LIKELY problem. The radio has four small holes on it. Two on each size - Vertical to one another. That is what you would use the coat hanger for -- Cut two 12 inch pieces out of a coat hanger wire cutters and form them into a U shape. Insert them into the holes and the radio should pop out. Removing the entire panel might require additional work. You can go to a local junkyard and test it out there.... And slip a few switches in your pocket while you're there.