Tachometer

Best guess. When the tach cable breaks a small piece of the disturbator cable ends up in the back of the tack. You need to replace the cable. And make sure the insert on the back of the tach is good and not stripped. To check the back of the tach. You will have to pull the instrument panel. You need to drop the steering assembly. Buy removing the two bolts under the dash. Then unscrew the panel. Once you do that you can pull it forward and release the tach cable. Use a mirror and flashlight to make sure that no other pieces are inside the tach. Reinstall new cable. Good Luck