Cruise control stopped working

They do this.

I have a collection of the circuit boards that mount under the dash, from junk yards, and changed them to fix it a couple of times.

If it is an auto, make sure the vacuum dump valve on the brake pedal is sealing closed when the brake is off. Not sure if there is a clutch switch on a stick car or not. But check to see if there is.

Make sure the speedometer pickup is plugged in, and there are not other vacuum leaks.

The last think I have replaced is the steering wheel switchs. It might pay to clean the rotary collector on the steering wheel.

Beyond that it need troubleshooting with a meter.