There are a few things you can check.
1. Check the vacuum lines under the hood (easy and they become cracked over time).
2. You can ohm out the
cruise control button on the column (doubt this is the issue)
3. The servo on the engine has 2 coils. It could be one of them has failed
4. Make sure your brake switch is not stuck on as that would not allow the CC to work
I will look, there was a website that talked about the "how to" on the servo. Helped me back in the day. If I find it again, I will post the link. The servo I found out is only for rebuild through Rock Auto (they were not able to rebuild mine) or you will have to find one in a junk yard.
Here is the website. You will need your voltmeter, but this helped me out!!!
https://www.motortrend.com/how-to/1506-how-to-diagnose-cruise-control-problems/