There are no specific fuses or relays involved in the cruise control system on your truck.
What is your concern?
Ok, that little tube is likely a vacuum line. Check to see if you have vacuum on that line and that it is connected to the intake manifold on the other end.
The 2 most likely causes would be a bad brake light switch or the servo itself which is what the little tube attaches to.
Here is a test for the servo.