The throttle with two orange and two brown wires is a non-variable speed type. Testing instructions for this throttle are attached below.
If the throttle tests good then we recommend testing the battery pack Voltage when the power switch is on and the throttle is fully engaged. The Voltage should start out around 27 Volts and should not drop more than 2 Volts when the throttle is engaged. If the battery pack drops under 23 Volts when the throttle is engaged then the controller will go into low-Voltage protection (LVP) mode and turn off the motor.
Please let us know how it goes.
One more test we would perform before replacing the controller is to unplug the brake lever's electrical cable from the controller and see if the bike works then. Sometimes the switch inside of the brake lever will malfunction and lock into the on position which tells the controller to stop the motor.