It could be the throttle, however, it could also be the power switch, circuit breaker, wiring harness, or brake switch.
Some versions have a normally open brake switch while other versions have a normally closed brake switch, so we would disconnect the brake lever connector from the controller and see if it runs then and if no luck then jump the controller's brake switch wire terminals together and see if it runs then.
If that does not help then we would test the power switch and circuit breaker for continuity and if they test good then test for Voltage at the controller's power input connector to make sure that the wiring harness is good and that the controller is receiving power from the battery pack.
Cathy Haggard