1. Hold cruise switch in the "set" position.
2. Turn the cruise "on"
3. Turn the main power switch on, the cruise light should initially come on then turn green, release the cruise switch the light will turn amber.
4. Push the cruise switch to "resume" the light should turn green, release the switch, the light should turn amber.
5. Roll the throttle "off", make sure you roll it off to activate the cutoff switch for the cruise, the light should turn green, release the throttle the light should turn amber.
6. Apply the front brake, the light should turn green, release it, the light should turn amber.
7. Apply the back brake, the light should turn green, hold the brake until the light turns amber, release the brake now, you should hear the cruise motor adjusting itself (taking ujp the slack).
What you have done is test each of the "switches" that are in the cruise system. If, during any of the tests, the light does not turn green, then that part is at fault.
The back brake switch is often at fault. You can test that by applying the brake and see if the light is already on. If it is, the cruise will not engage.
The front brake switch can be at fault also, as it sometimes gets damaged when work is done on the right handgrip/brake lever assembly and the proper procedure is not followed.
The "roll-off" switch can also be at fault. Check the connections on that.