The speedometer and odometer are controlled by the vehicle speed sensor on the transmission.
In the dash, there is a buffer that changes the signal from the sensor to something the dash can read. This was a common failure back in the day. I attached the location of the buffer for you.
The speed sensor for the transmission is on the output shaft of the transmission. I attached a picture and circled the area where the sensor is located.
Images (Click to enlarge)
Thursday, August 6th, 2020 AT 4:55 AM