my cruise control wont engage. what do i check

Try holding the brake pedal up with your foot when you hit "set". If that works, the brake light switch is out-of-adjustment.

Tug on the second throttle cable under the hood. It should pull up about half an inch at the throttle body assembly. If you get the whole thing in your hand, the cable is broken. That's not common. Check the vacuum hose going to the servo for cracks.

Additional tests are best done with a scanner that can display "inputs" and "outputs". It will show whether the various switches are working. There can also be fault codes stored related to the cruise control. Those codes don't cause the Check Engine light to turn on because they don't have an adverse effect on emissions.

The cruise control on my 05 santa fe would not work. The cruise display would not light up unless the brake pedal was depressed. As soon as my foot was off the brake it would turn off. My fuses and brake lights worked just fine. I figured that since I only had engagement when the brake was depressed that the issue was in the brake light switch. I replace the switch and now my cruise control works just fine. The part was $12.99 at Autozone.

That's a very unusual failure. Thanks for sharing that.