I have a '97 Mercury Sable ls v6 the speedometer, odometer, and cruse control stopped working in my car. I think that it is the speed sensor but I do not know were it is located at on my car or even if that is the problem.
The first to do is scan the computer memory for any trouble codes. Repair any codes that may come up. It sounds like from what you are telling me is that the speedometer, odometer and cruise control are not working. They all have something to do with the cable and gear from the transmission.
You can test drive the car and watch the vehicle speed on the scanner. If you have a speed signal then the problem may just be the cable from the transmission to the cruise control servo. If no signal is seen then the problem could be the speedometer gear inside the transmission and or the speed sensor.
Disconnect the cable from the transmission and cruise control and see if the cable is frayed or broken, move the cable by hand and see if it moves on the other side. If it moves then the malfunction may be the speedometer gear inside the transmission.
If the speed sensor was malfunctioning then the car may not work properly and set a code in the computer memory. Poor engine and transmission shift points may be affected if the speed sensor was bad.
This is not an easy repair, the engine exhaust Y pipe and oxygen sensors need to be removed for access to the speed sensor and cable.