Since the throttle has no indicator lights coming on that usually indicates a problem with the power system.
The first thing we would do is test the Voltage at the connector shown in the wiring diagram below. If there is Voltage where the red arrows point then that confirms that the battery pack wiring harness, fuse, and fuse holder are good.
Then we would test Voltage where the blue arrows point. If there is Voltage there then that confirms that the battery pack wiring harness connector and controller connector are good.
Next, we would disconnect the two red wires from the power switch and test the power switch for continuity. If the power switch has continuity when the switch is in the 'on' position then it is good.
Next, with the power switch on and throttle in the full throttle position, we would test the Voltage of the battery pack. It should have 27-28 Volts during this test, and if it has under 23 Volts then that indicates a problem with the battery pack or charging system.
To test the charging system start with testing the battery charger output plug's Voltage. It should be around 28-29 Volts. If the charger is working then we would plug it into the charger port and monitor the battery pack Voltage. During this test, the battery pack Voltage should very slowly rise. A digital multimeter will need to be used for this test.
If the charging system tests good and the battery pack drop under 23 Volts when the power switch is on and the throttle is fully engaged then that points towards a faulty battery pack.
If the throttle's indicator lights did light up, however, the motor did not run then we would test the throttle using the test described in one of the attached files.
If the charging system, battery pack, wiring harness, fuse, fuse holder, connectors, power switch, motor, and throttle all tested good then that would point towards a faulty controller.
Please let us know if you have any questions.