2005 Ford Taurus cruise control stopped working but light goes on when you engage the button but nothing happens and it will not maintain speed? What could have happened?

step 1
Remove the left sound insulator
step 2
the stop switch is here, way way up top
use flash light to see it.
it is there.
top of pedal it is there. SM books step1.

buy the service manual.?
if the switch ever sticks on , cruise ENDS
it is a NO, switch normally open contarts
no calibration is stated so its PnP

Bummer deal! This may be a way to tell you some tail lights are burnt out. Some cruise controls have a fuse in a second location.
The fuse is not in right or is blown. Check with a new fuse. Hope this helps. ...gc http://www.auto-tune-up-and-repair-options.com/

The first thing to check is the tail lights. The cruise control will not work if any lights are out. Changing to LED tail lights also causes the cruise to not work.

have a look at the cruise control cable that goes next to your throttle cable next to your throttle body for looseness

open the hood and check to see that the throttle cables are not out of place, if everything looks ok then unhook the cruise control cable from the throttle body (black plastic end) by pulling up on the cable end. this will disable your cruise control from making your car accelerate at unwanted times. sounds like there may be a problem with the cruise control servo.

my BMW 740i has a problem with the cruise control.
The cruise control will work for about 20 miles and then quit working and will not work again.

i've been told it's speed sensors. I have the same on my 1999, but my light flashes when i try to engage. And 1 out of 10 times, it engages and I can cruise. Just not worth it to me to fix. Ford never claimed there was a problem.

check the fuse of the cruise control that might be the problem or the alternator 

I have this same car. The place you set speed control is on the windshield wiper switch on the right side of the steering column. The button with the indicator light has to be pushed in order to use the cruise control but just because the indicator light is on, it does not mean the cruise is on. Hope this helps a little. If you need more info and someone else doesn't answer more eloquently.. I'll check back and try to give you more info. :-)