You probably have a bad speedometer switch.
Faulty vehicle speed sensor.
Most likely it is your speed censor modual. It is the wire that connects your speedometer to your transmission. It screws off and there is a wire connected to it. Replace this speed censor and you will get your overdrive back most likeley.
Where is speed censor on mercury cougar
The 1984 did not use a speed sensor are even have one.
Whatever they were ordered with, or whatever a previous owner may have switched them out for. Give me your transmission model, rear end gear ratio, and an idea of what sort of speed you're running at a certain RPM, and I can figure it out for you.
On the axles, just before the hub and brakes.
In the back end of the transmission.
Assuming you're referring to the speed governor, it's programmed into the motor's ECM.
If you're referring to the speed governor, there are no 'governor wires'... it's programed into the ECM.
The speed output sensor is designed to determine the speed of the output shaft. This sensor helps the transmission determine when it needs to shift for optimum performance.
The speed sensor is located on the back of the transmission, right before you get to the drive shaft you will see it sticking out.