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There aren't any fuses for the cruise control. The cruise switch input signal goes to the engine controller, and the controller's software uses the electronic throttle control throttle body to operate the cruise. Cruise control doesn't use any parts or systems that the rest of the vehicle doesn't use under normal operation, except for the cruise switches.
The most likely cause for cruise not working would probably be the switch itself. Cruise switches have given a few problems on different vehicles in the last few years. What will be done to diagnose your problem is a scan tool hooked up to see if there are any related fault codes stored in any of the modules, and then use the scan tool to monitor the switch states/voltages while pressing them to see if the inputs are correct.
With your Commander being a 2008 I'm assuming it's still under the basic 3/36 warranty. If it is, this problem will be covered, you'll just have to see your dealer.