Is it a 12 valve engine or 24 valve? What do you mean by speedometer sensor? Do you mean Vehicle speed sensor? If so why do you want to change that?
why does speedometer come on and off ?
A 1997 Mercury Sable came stock with size p205/65r15 tires. Taller or shorter tires will cause the speedometer to read incorrectly.
Inside transmission
The critical piece of information is missing from the original question: which sensor of the dozens of sensors in the typical Taurus / Sable
They don't have fuses. The speedometer is controlled by the speed sensor(s) and the temperature gauge is controlled by the coolant temperature sensor.
There is no Cable it is a speed sensor on the transmission
Have the speed sensor replaced.
It doesn't have one. It uses a speed sensor and drives the speedometer electrically. If your speedometer isn't working, it could be the sensor or it could be broken solder points on the instrument cluster circuit board.
remove the entire dash
I believe starting on the 1996 Explorer , it went to an electronic speedometer with a vehicle speed sensor ( VSS ) so it doesn't have a conventional speedometer cable
engine coolant temp. sensor
no cable electronic speed sensor (wire driven)