hi maybe someone came help my speedo only works at 65 mph the same gos for the curse control once you drop below that they go dead also when this started the ABS ,check eng,and brakes lights came on changed the speed control unt did not work ???
The Check Engine light came on? Did you scan the computer to see what codes came up? That might point towards the culprit.
Any chance the vehicle speed sensor is bad?
If this is a truck, then the problem is the speed sensor on top of the rear differential. Common problem that gives your exact symptoms.